It sounds like you plan to do quite a bit of work on the engine, but are trying to get by with using the old smog heads. In the long run I think you will find this is a difficult mistake to correct. You are giving up 30-40 hp right up front (vs. Vortec iron or aftermarket aluminum heads), and any future upgrades (exhaust, etc.) will not be as effective.
I don't know how to calculate the expected compression with new pistons and heads, but I there are several folks on hotrodders.com that could do it for you. You can also use different head gasket thickness to fine tune and change compression a tenth or two.
The 221/221 cam will work better with more compression, but GM managed to make a similar duration cam work in the 350/290 hp crate that only has about 8.2 compression. Its a bit of a dog, but it does okay if you keep RPM up. Unless you have good low gearing (3.73/4.10, etc.) and stock diameter (30-31") tires, you might want to go with a more conservative cam to keep your low end torque in a heavy vehicle.
Bruce