For what it's worth, we cc'd the combustion chambers on a #12 head (looks like it had one .010" cut in its life) and a truly never cut #216 casting date H157 (from a 1968 428HO/M21 Catalina) which became just #16 later in the year. The #12 measured 68.6 cc's and the #216 (aka #16) at 74.8 cc's. I imagine the #12 head started out closer to 70+ cc's originally.
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