I think most people like the 4 stroke engines better in this plane. I think the main reason is the inverted engine. The 4 stroke tolerates it better than the 2 strokes do. I would think the Saito 100 would be the best choice.

However, if you do use the FX91 it will have plenty of power to do anything you want with the plane including hover and 3D. I would use a 15x6 prop on it.

There is a huge thread over in the 3D forum if you want more info. If you go to the UCD46 thread all of your questions are welcome there. On both sizes of UCD (60 & 46).

Thanks
Barr;y