Agreed re the octane. We are not dealing with very high compression in the old engines.
On a side note , I used to have access to aviation gasoline. It had been drained from aircraft fuel tanks for maintenance and the standard procedure at that place and time dictated that drained fuel did not go back into the aircraft , thus the surplus , thus the great deal. Av gas has minimal additives and lots of lead. I'm here to tell you - that stuff made my older engines purr!
Av gas NEVER has ethanol added. The reason for that is : it can be very inconvenient when an aircraft engine stops running unexpectedly.
