I would suggest that you use magnum heads (typical 64cc's) for your build. The KB107 at zero deck, a 0.039" head gasket and the magnum head will give you 10.6:1 compression. I have this set up with an XE268H cam and it is very detonation resistant with the close quench magnum head. It will run on 89 octane with no audible detonation. If you go with the KB232 piston at zero deck and the magnum head you will have about 9.2:1 compression and might actually get away with regular 87 octane gas. But that XE274 would sure like the 10.6:1 compression.
NOTE: I chose the XE268H came just because the step up to the XE274 required a much stouter double spring and since my car is strickly a street car I didn't want to take the hit on valve train longevity you do when you start using really stiff springs.