RE: RCG 26cc gasoline RC engine
Just a couple of ideas for ya. If you have not yet, try some full synthetic oil @ 45-1. Also if you want to boost the engines performance put a Bowman ring in it. I've been running some test on normal oil versus synthetic. Synthetic runs a little cooler and give's a couple hundred more rpm. The Frank Bowman ring also boost the rpm by 2-4 hundred rpm's. And I feel a little more horse as well. With these mod increases you could increase the prop for more speed. Which is what you will need for the GeeBee.
I like what your doing keep it up.