I wouldn't be worried so much about the gas tank as I would everything else in the fuel system. Really need to make sure the fuel pump, lines, carb, etc are going to be tolerant to the ethanol and you need to make sure you have a robust enough of a fuel system to feed 30% more fuel. You'll want a good flowing fuel regulator too. It would definitely remedy your high CR problem, but I wouldn't go that route with a half a$$ed fuel system. I'm not saying your fuel system is not up to the job because I honestly don't know what you have, but just making a recommendation.
