Any chance the valves are incorrectly set and not closing properly when hot .

Made my pushrods from bmw R90 originals .

Valve clearance increases with heat thermal expansion is the term . In other words its not just the pushrod that gets hot everything increases in size thats why lots of valve clearances are set tight as they get bigger with heat . Other hot parts outway the length of the pushrod gains .  But this isnt always the case . I would do as you have and start big . If its noisy when hot then you can decrease it . I set my gold star to zero valve gap as everything is aluminium and the valve gap increases with heat , but , it could be completely different with cast iron .

This is the man .https://bsa.parts/ .

so starting from the nut you have the conical washer then the tab washer then the center then the basket nothing else . Does the center turn freely before you tighten the nut when out of gear .

your clutch drum seems to have a steel plate at the back of it so i wouldn't be too sure of copying the drawing you my have to start with a cork plate . remember the steel plates need cork plates either side of them the last one dosent matter as the pressure plate can act as a steel . Or it could be that there is already a plate in their .

You mentioned a domed washer next after the clutch drum . I cant remember that domed washer being fitted under the center . try it without it . If that indeed is how you fitted it .

Think you need to renew the rings and grind the valves in . should be between 80 and 100 psi not the greatest even then but at 4.5/1 its as high as you can expect .

I built a square four front wheel a few years ago and I struggled with the spokes until I realised that the rim was directional and I had I the wrong way round .

When I finished the rebuild on my DB500 I must have kicked it over 200 times and still no start . firing occasionally but no start . I double checked everything at least 10 times . I kicked it over that many times I strained my leg muscle and had to wait a week to get better . During that week i watched many videos on utube on how to start a bsa gold star . When i went back to it i used that information and it started 2nd kick . Now if it doesn't start first kick it starts on the second , even after 6 months , If everything is correct and it wont go  its down to technic .

mine is straight too . On another matter how is it you can see the reflection of the nut when it would be hidden by the bracket .

my front tyre is a 350 x 19 i think the rims changed from wm1 to wm2 when the tyre size went to 19 inch . Rear is 410 x 19 so mine must be wm2 rims . They are a spanish alloy rim .

Bought all my bsa db34 oil filter pieces from morgo ,https://www.morgo.co.uk/product-category/morgo-oil-filter-kit/ . They are the smallest you will find and easily hidden .

its still on the dvla register so is out there somewhere . last change of log book is 1979 so someone will have it in there garage .

cant remember which bike i was working on at the time but the amal monobloc was always leaking at the float chamber cover . It turned out the float spindle bush was too long and stopping the cover fully tightening . I even faced off the cover in the lathe as i thought it must have been warped but it still leaked until i realised that the bush was the wrong one . It could also be the float axel is touching the cover and holding it back from fully tightening .