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Depending on the quench you've got now, you really are better off milling the block. You'll never get close enough with the head gasket, and the quench (distance between the piston and head at TDC) really does matter more than most people think.

Most BBC's are setup 20-25 down in the hole. with a 39 head gasket that's 60-65 thou of quench. Way too much! You want it under 40 for good combustion and detonation resistance

It's really not that expensive in the sceme of things, and it's also a good way to make sure your deck heights are equal front to back and side to side as well.

PatriYacht , these are rectangle port that have been wedged to about 316cc and fully ported with some good flow #'s. they were done locally by a head guys who seems to put out some decent #'s, I think you know him.

Ok then it's worth taking a little time and getting it right.

Forget a thinner head gasket, it will account for next to nothing in raising your compression. What compression are you currently running, is this motor naturally aspirtated or supercharged?