We put an MC21 engine into a PGM1 88 chassis after thinking the crank was toast. Your crank is rebuildable if your pins and rods look good to the trained eye. see here http://www.nsr250.net/forums/viewtopic.php?t=7806&highlight=

All parts available from **** in Australia apart from maybe the thrust washers. Wiseco do these or you can recoat the originals in silver if they are not too farked. Not a cheap process but nice to start with a sweet crank.

From memory we used the PGM1 flywheel and pickups to keep the ignition timing the same. You can keep the GPS in place and just hook up the neutral...easypeasy. I found the correct colour wire off the wiring diagram on this site somewhere.