crispy, good work on reading up before posting your questions!
dfunkt has basically answered all your questions. Just keep in mind there are 2 different models of 5 speed, the only real difference is the gearshifter is in different places.
The 2 types are from KE55 (hard to get) and KE70 (common as muck).
KE 70 type has the shifter all the way at the back of the box, the KE55 one is forward further and I would guess probably fits almost bang in in the location of your 4 speed shifter.
TP.