[Mister Pontiac]

Originally Posted by Rocky Rotella

Thank you for the info!

So the question now remains, was "unstamped" used to denote the GP's 400 and base 428 4bbl cylinder head assembly up to a certain point? And was the "O" assembly that may have been dedicated toward GTO and Firebird 400 automatic applications eventually used on the on the GP's 400 and 428 4bbl, effectively eliminating the need for the "O" stamped casting entirely?

Great point, Rocky.

That theory would align with my engine (w/o stampings). It is indeed a late 67 build. F227 on the intake, although I haven't had the valve covers off since I installed it. Can't verify their date(s) at the moment, but I can safely assume they are close.