There are so many gearcases...!
4 synchro remote (Cooper S or Mini K)-
will fit any motor from 850 to 1275. So YES you are right, here.
Ditto the rod change boxes, both A and A+ types.
With the earlier 3 synchro ones it gets a bit muddy:
Early 850 and Cooper cases-
will take up to a 1098 crank, perhaps needing a burr ground off here or there.
1275 will not fit without major surgery- I did it once, but never again.
3 synchro Cooper 1275S box 12G333 has 1275, will take all others.
Morris 1100 boxes- the 1100S box has a 1275 stock but I'm not sure if the Morris 1100 casing is the same...
My recommendation is to forget the 3 synchro boxes for performance road use, these days- 1st or 2nd gear is easily busted with a 1275, parts are hard to get, and the boxes are not as strong as the 4 synchro ones.
