ORIGINAL: akaram

APC 16x4W will do the job. The 120AX mounts in the same space as the 90 or 60 so it all depends on the muffler you are going to use. With the stock muffler it will mount inclined with the cylinder tilted down, with a pitts it will mount horizontally with the exhaust port facing downwards.
As for hovering the plane, I have a 91FX on it with a 15x4W prop, it has unlimited vertical and i hovered it for some time far away up, it did hover very well but at that height I couldnt get a feel of how powerful is the escape from hover with full throttle. I am still afraid to hover low.