sj410 gearbox dilemma

[united1]

I have these 2 gearboxes. The small one is the original early (1982/83) gearbox and the larger one the original later model. Both will somehow fit to the engine (with some modification) and both are with 4 gears. My intention is to keep it as original as possible but the larger gearbox seems more robust . Can you give me your advise on what you think I should do.
p.s. I'm worried that since the small gearbox they had a factory problem, since it was in use for just 2 years.
thanks

[twiss]

I believe the smaller gearbox has a different flywheel and the pilot bearing sits in the end of the crank?
Whereas with the larger gearbox the pilot bearing is in the flywheel.

I think usually the larger box would be easier to find a clutch kit for.

[united1]

Thanks. It's getting more complicated then what I hoped .