I just bought my son the 03 RM65, its a KX with yellow plastic and it says Suzuki on it. I call it my Suzuki KX, manufactured by Kawasaki and the title says its a Kawasaki RM. (LOL)
Anyway I got a Kawasaki Race Performance Bulletin showing how to improve the performance of the KX65 motor, modifying the ports, cutting down the flywheel and extending the pipe, it also lists a part number for a new pipe if you don't want to cut and extend the stock pipe. Send me an email and I can scan the bulletin and share.
Steve