Depends on which heads they are - the round port E-heads come in two finished chamber sizes, 72cc and 87cc. I'd recommend either going a-head (ar ar ar) and pulling one of the heads to measure for sure, or checking for part numbers. I *think* mine have the part number stamped into the ends of the heads by the Edelbrock name, but don't remember for sure.
To really get an exact figure for compression you'll need to know the piston deck clearance anyway, and the heads have to come off to measure that.
Just "rough guessing it", 72 cc's with "usual" dimensions on everything would put you at 11.3:1 with 72cc heads, 9.9:1 with 87cc heads. (.040 gaskets, 4.18 gasket bore, .020 deck volume, 6cc's in the valve releifs)
I'd never recommend building a Pontiac that's ever going to see any 'spirited' driving without putting forged rods in it. Consider them relatively cheap insurance.
I love my solid roller cam, but they're on the pricey side so get ready - also if you go that route you'll want to put oiling restrictors in the lifter bores. Its not hard, I did mine myself, but you do have to thoroughly clean the block afterwards to make sure all the thread cuttings are removed.
How are you planning on driving it? --- Highway? Street? etc.