I hope I'm not leading you up the garden path here. I don't know much about these modern BSA's.
What is that ghastly looking mangled steel ring in the clutch hub? I suggest you remove it. There does seem to be some sort of "ring" here, probably as part of the hub, but it looks narrower than yours, and without a large chunk taken out of it. I imagine it's there to try to stop oil getting into the clutch. Maybe someone could post a picture of an original clutch hub?
In pictures 4 and 5, it looks to me that there is a grey friction disc fitted, with a beige friction disc fitted behind it.
According to the diagram, this is incorrect. Your clutch drum and the clutch discs should have friction inserts fitted into them. There are no friction "rings" fitted. These are only fitted on much earlier clutches.
Perhaps someone more knowledgeable than me can comment on the above?
 

3mm in English is less than 1/8" and will be quite useless, although when you get your spark gap tester, I imagine it will jump more than that. If you find it jumps 5/16", then you can forget about the strength of the spark and move on.
By 'vane' I assume you mean 'fin', but it's no good trying to hold the HT lead with your hand. You need to fix the HT lead so there is a gap of 1/4" and then 5/16" between it and the fin or vane, maybe with a bit of wire.
From what you have said, I get the impression you're not setting the timing correctly. Now it is all assembled, just connect your multimeter, turn the engine over in the correct direction of rotation on the compression stroke until the meter reads zero, and measure the piston distance. If it's 1/16" from TDC, your ignition timing is correct, and you can move on to the next thing.   

I think you'll find it's pronounced 'Rucas'.

My goodness me, what a saga. I imagine you will soon need a replacement knee and kickstart quadrant.
This may be nothing to do with your problem, but I'm not clear that you have quite grasped the ignition timing.
Since they started making motorcycles, BSA have recommended setting the timing on full retard, but since you're only interested what is happening on full advance (where the engine will spend most of it's time),what does it matter where full retard is? Once full advance is set, full retard will take care of itself.
I believe you have tried setting it on full advance, so could I ask how you held the cam in the fully advanced position against the springs? Also, how did you determine points opening? Test light or fag paper?
Sorry if this is a bit basic, but it might be worth remembering that the engine turns clockwise when viewed from the right hand side, and anticlockwise when viewed from the left hand side. You're not making the mistake of thinking the engine turns clockwise while you're on the spark plug side are you?
As has been suggested, get a pencil or spoke and with it in gear, rotate the rear wheel with your hand until you can see the piston rise to the top. Do check and double check that it's on the compression stroke and not on one of the other strokes. put the spoke in the plug 'ole and jiggle the back wheel until you can feel the piston is at the top of it's stroke. (This will not be very accurate, but it'll do for now.)
Holding the spoke on the top of the piston, turn the wheel backwards until the piston has PASSED your timing mark on the spoke (7mm up from the TDC mark.) Then turn the wheel forwards until your timing mark lines up with your fixed point. I use the back of the top of the spark plug hole. It's very important for the piston to always come UP to the timing mark and not down. This takes care on any backlash in the 'distributor' drive train. Now without turning the engine, and the cam held in the fully advanced position, use a test light or fag paper to establish the exact points opening position. Hold the 'distributor' and tighten the screw. Recheck the timing to make sure nothing has moved.
You once said it kicked back badly. This usually indicates the timing is too far advanced.
However, bearing in mind that the motorcycle started before you fitted the new wiring loom, assuming nothing else has changed, then either you have fitted the loom incorrectly, or the loom is faulty (which if it arrived into the UK on a ship, is quite likely.)
A few random thoughts. Quite often bad starting can be caused by a worn carburettor. I have never found a new slide makes much difference as it's the body which wears and distorts through overtightening. If you open the throttle a bit, you may be able to squeeze your little finger into the intake and see how much back and forth play there is in the slide. Don't open the throttle too much, as the most wear takes place at small throttle openings. Maybe you could use a bit of bent wire? There shouldn't be much play at all.
You mention it pops sometimes. Do you mean fires? If it does actually pop, this indicates an ignition problem.
Moving on to your Monobloc, you need to make yourself familiar with the Pilot Bypass and the Pilot Outlet. These are the 2 small holes in the inlet tract either side of the slide. The best  way to physically check these are not blocked is with an aerosol and extension tube. A sonic bath may not clear these.
I believe you have disconnected the feed wire to the points and connected a separate wire directly to the battery, not to the headlamp switch? And still it did not start?
Your compression is a tad low, but it should still start.
You said you purchased a Spark Gap Tester, but you have yet to tell us what gap the spark could jump. Or did you mean you bought a neon tester.....not the same thing.
Perhaps you could let us know the answer to these questions, and we can move on to further suggestions.

No O rings or seals were fitted.
Yes, the tappet guides are just screwed in tight. I'm sure you know that the guides are locked by tightening the 2 long timing cover studs with scallops in them, so these go in first before you fit the guides.
You could fit a fibre washer at the top, but I've never found the need for one. Very little oil gets up there.
The Parts book shows 2 coil springs per pushrod. BSA call the heavier one a push rod return spring, and the lighter one a tappet tube spring. It would seem that the lighter spring would be at the top, simply to hold the upper pushrod tube in contact with the rocker box, and the heavier one would be fitted to the bottom to hold the pushrod in contact with the tappet/cam.
Manufacturers at that time were overly concerned with keeping the tappet in contact with the cam, hence the additional springs on the rocker arms.
The idea is that the spring tension of the lower spring could be adjusted by screwing the lower pushrod tube in or out as required. It is then held in position by the double eared spring clip locating with the groove in the pushrod tube. Therefore the pushrod tube is not tightened fully down onto the tappet guide. If you find it necessary, you could apply some Red Hylotite to the threads.
I hope this helps.

What a strange motorcycle. It seems to be a Bitsa.
I do not recognise the gearbox at all, but I'm sure someone does.
I'm sure JABBA is correct in identifying the engine.
If it's a vintage BSA frame, the frame number may be under the saddle on the left side, but have a close look all over to see if you can find a frame number.
Someone has fitted covers to the valve springs.
I see it has a duplex primary chain, so the clutch is much later.
I wonder if you can spot any welding on the frame on the top and bottom mountings for the plungers, which look very aftermarket to me.
The bottom of the headstock looks like a thin steel cover, and the knurled ring is odd.
I'm sure the rear brake drum and backplate are not BSA.
Oil would be fed by gravity to the Pilgrim oil pump, which would drip feed oil into the crankcase, and be splashed about all over the place by the flywheels. Don't forget to turn the oil tap on before you start it.
In the'30's BSA used a left hand twistgrip for the ignition advance, but someone has fitted a later drum twistgrip.
It seems someone has welded a hump onto the petrol tank, and fitted a cajones protector to the back of the tank.
Does it run?

I wonder if you have seen item 396528234843 on Ebay?
The Part No is correct for your machine, and it looks correct, although the seller says it's for a Sloper, which it's not.
Let us know how you get on.

If you are concerned about washers, you c0uld have a look at Hitchcock's website and search for 140771 Timing Cover Screw Fibre Washers. These are tiny 1/4" ID washers that some manufacturers fitted.... (Royal Enfield?)
They're probably not necessary, but it's up to you.

I wonder if you have a lathe and welding facilities, or know someone who does, if you could make a fulcrum pin and adapt a lever from another motorcycle?
I imagine BSA hardened the pin, but perhaps you could use EN16 or 24? You could weld a 2nd arm to the pedal for the return spring, and maybe drill and tap the pedal boss for a grease nipple?
A lot of Blue Stars had a foot change gearbox, with the brake pedal on the left.
I swapped my 250 Blue Star brake pedal to the left, but unfortunately you need a cross shaft, which is a very rare item. This has a square on each end, and if you can get one, you're laughing, because you can then use a C10/11 brake pedal, shorten it, heat it and bend it to shape and weld the pad back on.
I found that BSA had very kindly fitted bronze bushes to the two frame lugs, and I just had to make up the spider lever for the other end from the picture in the Parts Book. It all works well.
It's just a question of whether you can get the correct pedal or the cross shaft. A C10 pedal is easy to obtain.
Just a thought.
"Yesterdays" have pictures of a 1932 hand change W32-7 Blue Star, but doesn't show the pedal very clearly.

Well done, that man.
If you could post a screen shot of page 142/3, this will show Mr. Hot Frog what the other parts look like.

I am not surprised you are confused. I don't know much about this particular model, so perhaps others with more knowledge can assist further.
Your photograph shows the brake pedal and stop plate (at right) for the ubiquitous Sloper model.
Your brake pedal should have 2 arms on it, 1 presumably for the brake rod, and the other for the return spring.
There is a pin in the inner face of the pedal, which engages with the pedal stop plate 27-6337. You also need pedal spindle 27-6336 which is bolted to the frame lug.
I have no idea what the other 2 parts in your photograph are, but I don't think they are used on your model with right hand pedal.
The return spring is just an ordinary expansion spring with ends at right angles.
You really need a Parts Book to identify these parts, but I will try to post photos when I work out how to do it, if this would be of any help?

I agree with scifi, although I would take 0.003" to 0.004" as being absolute minimum clearances.
Also, be sure that valve stem and guide bore are clean and oil free before checking clearance.
Cast iron is the only material to use for Sloper valve guides.

Dean, You will be pleased to hear that F.W. Thornton have Sloper pistons in stock, but they don't seem to appear on their website.

Although Service Sheet 15 is dated September 1930, I believe it only refers to pre 1930 models, where of course, the ball bearing is against the flywheel, and it's talk of Glut Pins, which were deleted for 1930.
It's interesting to note that Bernal Osborne was also a little confused about the positioning of the bearings, in his article for Motor Cycling Magazine.
He mentions that a previous owner had swapped the position of the bearings, (i.e. from the 1929 arrangement to the 1930 arrangement.)
He goes on to say that the Artist has reproduced the BSA drawing, but fails to mention that the drawing is clearly of the 1929 engine, complete with inner spacing collar and Glut Pins.
It seems that BSA themselves got it wrong, because if you study the OHV engine line drawing on page 13 of the 1930 BSA Motor Cycle Instruction Book, you will see that the arrangement depicted is of the 1929 engine, with the ball bearing against the flywheel, and inner spacing collar. So it seems that the different departments of BSA were also confused.
In practice, I doubt if it would make any difference how you fitted what bearings, as long as you didn't use 3 roller bearings. If fitting a ball bearing against the crankshaft with an outer roller bearing, you would need the inner spacing collar.

Aha! I think I have just had a Eureka moment. More of which later.
Since you're doing the 1930 engine, I believe you are using the incorrect roller bearing, which, of course, gives rise to your question about the possibility of the inner race moving towards the ball bearing, and the consequent need for an inner collar.
I think, if you search on the internet, you will see what N305W and NF305 look like.
Yours has only one flange on the inner race. Mine has 2 flanges. So can you now see that the inner race of the NF305 can't go anywhere, and there is no actual need for the inner spacer?
The Eureka moment I had, was that I discovered that for the 1929 engine, BSA transposed the bearings. i.e the roller bearing goes in first followed by the 2 collars and then the ball bearing. Hence the need for the inner collar on the 1929 engine, but not on the 1930 engine. Ta Da! I suppose you could phone the Factory for advice, but I tried the other day and there was no answer. (Sorry about that.)
So, if it was my engine, I would swap out the N305W for the NF305, and forget about making a collar. It's up to you, and I seem to be in a minority of one.
I couldn't find the Sloper piston on their website either, in fact, I couldn't make much sense of their website at all, but if you email them I'm sure they will put you right.
As I tried to suggest, checking the endfloat is really very simple. Just assemble the crankcases and push and pull the mainshaft in and out with your hand. To be accurate, it really needs to be done with everything dry, as oil will take up clearance. No need to put the cush drive on, or the 1/2 time pinion and nut. Simply push and pull on the drive side mainshaft. That is your endfloat.....if any. There is no thrust face to pull up against (as you say), because the cush drive is on a taper and not up against the bearing (as Mr. Chapmast says,) and I'm fairly sure the 1/2 time pinion butts up against a register on the mainshaft, and does not tighten against the bearing. But it's minus 10 degrees here at the moment, and I don't want to freeze my balls off going outside to check.  So, NO, NO, NO, the cush drive does not lock up against the bearing (again as Mr.C says.)
As you say the Sloper crankshaft can float around, and that is why BSA recommended zero endfloat (less 0.002"), as per Service Sheet 15. Personally, I wouldn't bother about the 0.002" nip.
It would be good to know if you have now got your head round it all.