I am flying one (the aluminum finsih) with a TT .46 Pro and it has more than enough power. It will keep up with any .60 on the field. With the wheels up and tucked away, she will do just about anything. Snaps, rolls, spins, etc. Yet she will still slow down and land like a trainer. So far no probelms with this plane. I did have to mount the engine upright, becasue I had some probelms with cooling. Another guy at the field has one with an OS 70 four stroke. It sounds great in the air, but mine is faster. If I were you I would stick with the recommended engine for this plane. The heavier 4 stroke or larger .60 will stress the landing gear. I fly from grass and to this point have had no problems, but I would be leary of adding additional weight, when the .46 will be adequate. Albeit, the OS46LA is not quite as powerful as the TT, but it will close enough. Run a 11X7 prop and try it before you add something bigger.
Tommy