I cc'ed a 516 head once that had hardened exhaust seats and 1.74 valves installed. I seem to recall it was 78.5 cc (NHRA Blueprint spec from the Direct Connection book was much smaller, something like 73 or 73.5 cc).

You need to measure the piston deck height and the head gasket thickness. That will tell you what head cc you need for a given compression ratio... what do you have now?