Did this quite a few times, get the entire 5 speed internals including the selector. Put the whole lot in the 4 speed case. If you use the 4 speed selector you will wonder why every 5th[?] gearchange is a neutral..
It's about 25 years since I did the last one, I can't remember there being anything to do apart from reasemble with the 5 speed bit's...
I used to come across quite a few people who had rebuilt boxes with the 5 speed internals and said it didn't work saying something like "you get loads of false neutral". That was cos they used the 4 speed selector bit's..
