old thread... but i have to say, i own a 83 and a 97 kx250 thats similar the same as your 84 to 98 question
if you look good, you´ll see the motors are not identic ...only the standard bolts and nuts you can share between them.
crank seals and con rod are equal used in the kx 250 from 1980 up to 2008 (same oem part numbers)