By the late 1950's/early 1960's, even "regular fuel" engines had compression ratios in the 9's, so gasoline needed lots of anti-knock compounds. Some of the super-premium gas was well over 100 octane, and I've seen stock compression ratios of 10.5:1 or more on some of the factory hotrods from the early 60's. Other than buying 100 octane aviation gas or a few "off-road only" brands of racing gas, I can't imagine running those engines without some sort of fuel additive, even on unleaded "premium".
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!