G'day Dan,
i will happily stand corrected if its proven to be A RC500. i think the defining characteristics that will give an RC 500 up are the Engine and Frame numbers will be unique compared to the Production CR250's. also lots of small details, like gear levers and brake pedals, brake actuation arms etc will be machines from Billet aliminium, titanium bolts here and there.
it is a very nice bike , have you or are about to buy this machine ? and is it located in Australia?