I am guessing that's the stamped number on it - does it have a two letter code?
I ask because I jest went and looked at the spare pulleys I have, and I do not have that number.
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1970 Formula 400 Carousel Red on black (std) interior "no drivetrain option" car (same base drivetrain as GTO) 1:411 1970 Firebird Formulas originally sold in Canada