My father and I have a lot of cars and they set for long periods. None were ever ment for ethnol fuel so I run and store them with 110 octane aviation fuel. It has all the stuff in it that will not gum up anything. Most of my cars, '64 Mustang covertable, 2 '65 Mustang Fastbacks, '79 Formula Firebird, and even my '67 Econoline love the extra kick. I either drive them to the airport or fill some cans. Expensive but no problems with it for years.
My friends P-51 Mustang runs on 110 too!
I wish I had a friend with a P-51 mustang... haha. Cool piece of history.