I looked at one the other day at my LHS. Very cool little engine. Can you fit the Zen G26 into the H9 Hellcat? What about that extra weight? It would be a shame to add all that extra weight in the tail just to get your CG right. That extra weight would also kill those retracts for sure, and you better reinforce that firewall or you will be flying Santa's sleigh without Rudof.

Zen 20cc = 41.6oz w/muff and mount
Zen G26 = 59oz w/muff no mount
Saito 100 = 20.9oz w/muff no mount

I'm really thinking about putting in the Saito 100.