For what it's worth, I ran the flow characteristics (as best I know them) of the 12-port head through an engine simulator that had been tuned to match the results of the dyno tests by Frank McGurk in the May 1955 HRM. The results indicate that, if one has the nerve to take a stovebolt crankshaft and valve train to 6500-7000 rpm, the peak HP gain could be 60 to 100 HP.
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