That is a great question. Back in the 80s I would use the highest-octane leaded gas I could find, and THEN add octane boost (and lead substitute after leaded gas became scarce). It helped tame the pinging when accelerating somewhat, but not the after-running problem. You could switch the key off, put the trans in first, and drop the clutch, and if you didn't have your foot hard on the brakes, it would squeal the tires and leave a skid mark before the engine stopped. I wanted to try Av Gas--115 or higher if possible--but I never got hold of some from the local airport. I think I have found a local supplier of Sunoco racing fuel, which will be great if it's true, but right now, while I am setting the timing and carburetor and adjusting things, I am using 93 octane unleaded (of course) with Lucas octane boost and Red Line lead substitute, for the valve seats. This engine runs great when you advance ignition timing a lot. The downside of that is the pinging under load, and the after-run, and the hard re-starts on a hot engine.