This is not something you can assume or guess on. Combination of dome size, base gasket thickness, squish, timing, and elevation all play a role in determining the octane you need. So, you need this info to determine what gas you need to run. Even a more stock motor can benefit from running 100 octane 50/50 race gas, it will run cooler. If you somehow ended up over 175-180 psi compression, or your squish is out of spec you can end up eating a piston as a result of not enough octane, or improper squish tolerances.