[68post]

"7cc" is usually just the amount the valve reliefs contribute to a true "flat top" piston, you'll never achieve 10-1 with a dished piston and 64cc heads with only 355 ci..( in other words..if you have a dish and valve reliefs..then you have way more than 7cc to account for).
Please do not consider thicker head gaskets to lower compression, there's very little leeway when adjusting gasket thickness if you are staying within proper quench distance.

If I remember correctly a 383 only achieves about 10.7-1 comp with a flat top piston and 64cc. (5cc to 7cc for valve reliefs, and proper quench)

A '96+up vortec has a slight dish and is only 9.3 rated @ stock 350ci with it's claimed 64cc heads (not sure if it would measure out to a true 9.3 !!)