TR25W and TR25T gearbox mainshaft

[Tigerfeet]

I am trying to get my facts straight regarding the gearbox mainshaft in the later 250s - specifically the TR25W (B25) and TR25T (B25T / B25SS)

Having perused the Rupert engine book, it seems that the 1969 engine had various weak points. These are all related to the crankshaft/conrod/oil pump. I have managed to obtain a TR25T engine from March 1971, with all the improved items. But it has no gearbox, primary drive etc..  I was hoping to transfer these over from my dismantled 1969 TR25W engine.

According to the various 250 parts books, the 1969 engine has a 57-2661 (BSA 40-3254) gearbox mainshaft whilst the 1971 model has a 57-4344 mainshaft. (This appears to be the only difference between the gearboxes.) So my question is, are these interchangeable? Or do I need to find a 57-4344 shaft?

[Tigerfeet]

Question is now irrelevant. The TR25T engine won't fit in the earlier frame. So I will be rebuilding the earlier TR25W engine using the later crank.