This is nothing new....Crower as an example back in the late 70's (IIRR) had a new cam grind that could run up to 11:1 CR and still run off 91 octane (which was the best you could get in SoCal). It's all has to do with cam/crank timing, the quench and materials used. There may be more left but each engine has to be carefully looked at as far as how they accomplished it.
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Flatheads ain't so bad!
Certified backyard mechanic I & II