About 14 years ago I lived 1 mile from an airport. I used to run aviation fuel 100LL (100 octane low lead) in a 13 to 1 BBC. Never had a bit of problem with it. Now I did have to go up (I think ) 2 jet sizes on my carb. Since 9-11 I don't know if they will still sell it to the public. If it's available to you, I wouldn't be afraid to run it in a 12.5 to 1 motor.
TS1955