Bantam D13

[RCS]

I am trying to put back together my late brother's D13, it has not been on the road since '79 when he took it apart to try and get it to run properly, had been in the corner of his garage in boxes ever since.
I will try and explain what l have done so far
I put the gearbox back together with a little help form a Haynes manual's and internet
The layshaft was complete with bushes so l left it as is, sorted out the mainshaft gears, noticed references to 21 and 22 tooth sliding gears. looked on YouTube to see how the gear selector was fitted, with that put the two half's together, easy!, tried the gears, bit hit and miss.
Took it apart again, paying more attention to the gear selector and sliding gears, Put the 21 tooth on the layshaft and 22 tooth on the mainshaft, tried to close the cases, nope !, noticed the layshaft wouldn't locate into the layshaft bush, this went on for sometime
If l took off top gear from the mainshaft they would fit together, but no matter what l did the top gear would not slide through the bearing while on the mainshaft, in desperation l change the two sliding gears around, 21 tooth on mainshaft, 22 on the layshaft,
The cases now fit together, and l have 4 gears, in the Haynes manual there is no reference that l can find to the number of teeth on the sliding gears, just an exploded drawing  of a 4 speed gear cluster
What have l done wrong !!, can someone with far more knowledge than l tell me what

[V500]

Bound to be trouble, it's a D13!
I had one for a short time (KBK 990F where are you now?)  and never realised how rare they are until after it was sold.

[JulianS]

Below 2 pages from the parts book shows the teeth per pinion.

[RCS]

 The 21 tooth is fitted to the layshaft, and 22 to the mainshaft, so l had them the wrong way round, that pushes the lay and main shafts out of vertical, information found, there may be an oversized gear somewhere

[RCS]

Gearbox now assembled with all the gears in the right order, found that the 25T and 26T pinion were both in the wrong places