[Mister Pontiac]

Originally Posted by Rocky Rotella

• “O” denotes Grand Prix’s 400 4bbl and base 428 4bbl specific 670 assembly.
• “(blank)” denotes 9787603-specific 670 assembly for AUTO trans GTO and Firebird 400s and 428 H.O.
• “Z” denotes 9787608-specific 670 assembly for MANUAL trans GTO and Firebird 400 and 428 H.O.
• “X” denotes the Ram Air-specific 670 assembly for the 400 Ram Air option in GTO and Firebird.

This is simply my best guess at this point. I cannot claim any accuracy just yet!

Thoughts?

Rocky,

Just to add in another bit of possible confusion, I have a base YH 428 out of a 67 Grand Prix that appears to me to be blank (no stampings). I double checked again today just to be sure, and I can't find any stampings. The heads do have some rust on them, but after wire brushing the area, I cannot see any remnants of a stamping on either head. So...

To the best of my knowledge, this engine has not been apart since it left the factory 50 years ago. From what I understand (from a fellow PY'er I bought it from), it was pirated from a 67 GP back around 1971 following an accident that destroyed the car. After that, it sat in two different garages for 40 years untouched before I bought it and installed it in my wagon. It still has not been apart.

So if its history is accurate, mine in a base 428 out of an automatic GP, yet it has no stampings (blank).

Hmmm...