[steve25]

I compute your compression at a best of 8.27 to 1 assuming that your Pistons have a valve notch volume of 4 CCs.

If you mill your heads down to 79.5 CCs you will then have a 9.3 to 1 compression.
To get there you would have to mill .060" off of your heads which is doable.

I used a common Fel pro head gasket in my figuring of your compression ratio and it spec's out at 9.4 CCs, but I believe stock replacement types are smaller and might help to up your ratio.

To get the Intake Manifold to play nice with the milled heads you will also have to have the Intake flange of the heads milled at least.045".

If your heads have already been rebuilt I would consider this as a option, if not then look for other heads.

Milling .060" off will not be cheap unless you have a good in with a machine shop, or do some horse trading, hey you never know so there's no harm in having that chat .

If you have a few shops to choose from, call around and get some prices.

Do not toss out you stock heads however, as there a good head for someone with a 400 , 421 or 428 motor.

These 7HI heads are the only Pontiac heads ever made with the 1.96" / 1.77" valve size which makes them a great pick for stepping up to the 2.11" valve and then use them on the above posted motors to get under 10 to 1 compression.