There are 400-specific features on the car but those can get added/removed in 58 years; hood scoop hood, grill chrome "L-shaped"(aka hockey stick) instead of straight, hood and trunk 400 emblems, chrome valve covers (instead of painted), front bumper Pontiac arrowhead. The '68 air cleaner has a chrome lid. I don't recall for the '67.

If the engine is original it will have the codes, as shown on: https://firstgenfirebird.org/1967-i...n/1967-drivetrain-id-number-information/ However, engines can be replaced. I believe the VIN stamping on the engine only began in '68 so the confirmation of originality can only be done with the engine serial number verses the PHS.

The trans numbers and type are also found on the above page.

However, the only sure way I know how the original equipment is ordering (for a fee) the as-built documentation from Pontiac Historical Services (PHS).