I have a carbureted Corvair. I add a small amount of marine two
stroke oil at each fillup (I try for 200:1). The aluminum heads have
inserts that are perfectly fine for unleaded gas, the oil is for
shutdown. My next engine is under buildup now, and will probably have
EFI-what I really want is a mechanical speed density (K-Jet is that-so
is the Bendix system on Turbo Indy Offys and TIGO Lycs) system with
electronic trim, but it's way more time, energy, and blown testbed
engines than I have ambition to fool with.

I looked into propane as well, but range, cost, and fuel availability
in the U.S. are all nonstarters. Plus there is no coolant for a
vaporizer on a Corvair.