[steve25]

Something rang a bell in regards to these 670 heads and 428 motors!

I went back and looked in Pete McCarthys first book and on page 39 the 376 hp 428 is stated as coming with two different valve spring set ups, one for the standard Trans cars that have Exh springs with a higher pressure , and then a set up for the auto trans cars.

The factory would have needed a way to differentiate between these assembled heads and maybe that's where the Z and the o stampings come into play?

The 360 hp 428 seems to use the same pressure springs across the board between the standard Trans and auto Trans cars which would lead me to believe that both these 360 hp 428 motors and the non RA 400 motors would get the same springs and hence the same stampings .....?

Now to prove this out and then prove out which stamping code goes with the 376 Hp standard Trans 428.