I need a crankshaft for a 75 R90s.  This brings me to several questions.  How can I identify a crank as being compatible for my needs?  Further, how can I determine if a crank is from a R75, R90, etc.?  I'm also going to need a cam which brings up similiar questions.  For a little back ground, I bought a one owner non-running R90s with 40,000 miles.  The older original owner said it started making an odd noise many years ago.  Took it to a dealer, they partially disassembled it and reported it needed a crank.  At that point the old boy parked it as he had multiple BMW's to ride.  I removed the crank and it is in fact cracked!  Cam is also corroded beyond use at the snout.  I have some R75 and R80 stuff, just doubt any is compatible?