dont hold me to this but iirc all 5 speed boxes are the same (attachment wise). and theres only 1 type of 6 speed box
i believe the differences in the 5 sp boxes is the ratios, and also the gear linkage, so in theory you could fit any 5 speed box, however, ratios will be different and i believe you may need to take a few parts off old box such as the selectors or other parts...
however i could be completely wrong so dont hold me to that...