Since you didn't indicate heavyweight or streamline car, here are both:
For heavyweight,
Standard heavyweight car, dulux gold lettering = P-2
Standard heavyweight car, bronze gold lettering = P-2B
Heavyweight EMPIRE BUILDER, pre1947 era, bronze gold = P-130
For streamline,
Streamline dulux gold (EMPIRE BUILDER letter board) = P-45
Streamline dulux gold (other than Empire Builder) = P-122
Note: car names unique to each of the streamline sets included.
Good luck in finding ANY of these O Scale Champ sets!