adrenalnjunky,

Yes, I had the 25cc GT on this plane and have swithched to the 26cc SS. I bolted the 25cc GT right to the engine box and ran bolts from inside the engine box through the threaded mount. The 26cc engine was a little smaller and had a plate bolted to the back side and the distance from the engine box to the back of the back plate on the spinner was the same. Just mount your cowl so you have a 1/16 gap between the cowl and the spinner back plate. Mounting the engine this way the CG came out to the print which is correct. You might run a few tanks through it before you fly. They gain power with more run time on the engine.