Rebuilding engine/ head gasket compression question

YES! The year of the 360. The pistons are low in the block. The factory used the thin gaskets regularly. You can't go thinner, only thicker.
IMO, I really realy suggest a new set of pistons. Fed-Mougal makes a nice 9.5-1 coated skirt piston and KB makes a few as well.

Increaseing the compresion ratio will make the roatating assmebly lighter so it can spin faster, easier. The increased ratio will add some power. Zero deck the pistons with a .039 gasket with the big chambered "J" heads will get you 9.8-1. .054 gaskets will drop it a tad more to approx. 9.5-1.

Zero gap piston rings are expensive, but worth the price. Extremely low leak down rates.

And what was said above. Just tell your machinest you want a million mile engine when your done.