i have a rebuilt 350 sbc, bored 30 over with unknown pistons(still runs on 87 octane), 333882 heads w/76cc chambers.  would like to know what the compression change would be if i swapped some 14014416 heads w/58cc chambers on.  

This question cannot be answered accurately without knowledge of several variables affecting the compressed volume of each cylinder (piston/deck height, piston dome/dish, head gasket bore, head gasket thickness). Moreover, the cylinder head combustion chambers would need to be cc'd to determine the actual volume (as opposed to the advertised nominal volume)

But making an educated guess about the unknown variables (which is about 95% of all internet technical discussions about automotive topics), the compression ratio with the 76 cc heads should be in the range of 8.3:1 and should be around 9.9:1 with the 58 cc heads.  Obviously these guesses are way off if your "unknown" pistons have a big dish or dome, or other factors add or subtract ccs from the combustion chamber.