I powered my "Pro" with the OS 1.20 4 stroke (pumped inverted). I haven't test flown it yet, but the engine does fit well in the cowl. However, the muffler, IMO is a little too close to mother earth and I am a lttle concerned it will hit the ground with a less than perfect landing. If I were to do it again I would consider mounting the engine horizontally, although the cowl would need a little carviing.

DaveB