You need to get a copy of your original factory documents from Pontiac Historical Services. Your main concern, having the original engine block, cannot be determined exactly without those documents.
Pontiac did not stamp the VIN number on the front of the engine block until sometime in the 1968 model year. However, your PHS docuements will have your unique Engine Unit Number which IS stamped on the engine block and can be used to verify if you have the original motor.
You can use the number crunching info from this site to verify cylinder head and engine block codes along with date codes for the other drivetrain components.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
