Perhaps the original engines were but the conversion changes the cam, compression ratio, and timing curve. My engine calls for 93 octane as a minimum but slight reduction in timing would allow a lower octane. With that I'd have to give up some power (probably in the 2% range).Corvairs were designed for 87 octane weren't they? Clark's corvair says they'll do fine on ethanol blends too.
I believe everything in my system is ethanol resistant but not sure about the carb as it's a Marvel Schebler from an O-200. Besides, I just think it's wise not to put ethanol in my airplane. There may come a day but it ain't here yet.