EFI makes this much easier.
I would personally only run drum E85 if carbureted rather than chase the alcohol content.
Why?
Our local pump E85 use to vary from E75 winter mix to E85 summer mix, I learn to buy enough of the pump E85 in the summer to last my racing year, 30 to 60 gallons
I would fill all 6 of my 5 gallons plastic fuel jugs and let it sit in my race car enclosed trailer over the winter and it would check from E86 to E89 % the next spring, I would mix a little of the current year pump E 85 to bring it down to match the E85 tests
