Again: Unleaded or leaded fuel for mid 70's /6?

Aviation 100 Octane Low Lead at your local airport
Hope Your mixin' that with normal fuel, avgas runs like **** straight, not meant for cold starts/operation at ground level. I had a customer dump that in the tank of His MonteSS, World Product headed 350, Street Avenger Holley. Would barely start & run on a summer morning. Not to mention 100 octane is 14 points too high for a stock Slanty, & their rousing high 7's squeeze. OP, Your seats are induction hardened, & You can run the equivalent of 87(R+M÷2) here in the States.