Hi Nip, yes i have made what i call REM250B's and have built numeous RM ENGINES as i raced RM's as a pup and worked for kessners back in the old days,all RM components will fit PE but PE gearbox will not fit RM due to the Pe cases being machined out for the larger gears. now for the parts you will need to make a PE into a RM (REM) RM250- head, barrel, crank shaft, gearbox, stator plate rotor and PEI pack as the curve rate for ignition advance rate is differant to PE, carby and or replace all the inards with RM carby specs, all the best on your quest, if i was you i would buy that RM engine offered to you,
cheers