If memory serves me correctly the last GeeBee I built reguired more nose weight than one may think. You fellows may want to put it together without an engine and see how much weight/engine will be needed to balance. If you think about the real plane you will see that they had a huge powerplant hanging off the firewall. My guess is a gas engine will work, within reason of course. Plus the benefit to using gas is the fuel tank can be located on the CG if need be.