are you looking for the correct stamp, or size? many wheels of different stampings from different years are the same size.
http://www.pontiacserver.com/wheels.html
it seems contradictory to me to be concerned with codes for originality, but finish the wheel in a non-factory manner (just sayin'). i'm a huge fan of powdercoating, but don't think wheel codes are a big deal, either. you will have to remove the powdercoat (which isn't cheap) to know beyond any doubt of what the code is.