RE: Zenoah G38 on Giant Big Stick?
The G26 and G38 end up making really close to the same thrust on their respective best props and common aftermarket mufflers. The 26 converted to EI and running a Macs tuned pipe would sway the decision for me significantly between the two engines, but that's not what's on your plate right now. A good deal on a brand new engine that is suitable for your project is hard to pass up! Keep us posted!
Chad