This really would work better in the "race" section.

What Stage VI heads are they? I know you said MP but that doesn't help that much.

Some Stage VI heads were cast to allow use of a 440 intake on a 383, then you had to use the spacers to use a 440 intake on a 440. But I seem to remember they also had some Stage VI heads that were straight replacements for the 440.

Also, although I'm assuming you're talking about a 440 or other RB, what engine are you talking about?

R.