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depends on what engie you put the heads on and what year engine, different years and applications of same size engines can have different pistons to work with heads with different combustion chambers volumes to achieve compression ratio goal of GM at that time. different pistons were used o soem, some with deeper or ore or less reliefs, or less or more head height, etc etc. some engines were 8.0 some were 8.3 some were 8.5 and sem were 9.6 and some were 9.0 and some were 9.5
the L69 305HO(factory 350 Vette camshaft- the 190 horse 305) were 9.5 CR and the LG4 305 of same year(base 4bbl 305)were 8.5, for comparison purposes
most 8.5 CR engines had 75 or 76cc heads,. there were both, the there were 70 and 58 and another one,
changing valves sizs or thickening seats or milling down head deck gasket surface etc will affect volume of the combustion chamber and therefore the CR of the engine.,
could go on forever, there are aways HUGE discussions over this and everything else at places like thirdgen and chevytalk and so on and so forth.,
head work is $$$$$ to have done, personally id just find a set of good/better ready to run heads of some kind- older or later- even if you have to get a different intake, i have found a set good stock 1990 350 TBI heads i am getting tommorrow for use on a '85 350 bottom end that i have here that i want to have ready to run, only 'cuz can get them alot cheaper than any caveman{carbureted) heads (ones that that arent completely worn out and needing rebuild, guides, seats valves, etc)
even stil cheaper even after intake purchase in order to be able to use carburetion, if not cheaper, then damned close
good luck
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