RE: Inverted Engine
I think the CofG thing is part of it, but in most scale type planes, the prop shaft is closer to the top of the cowling than the bottom. So the choice is a small amount of engine sticking out the bottom, or a Lot of it sticking out of the top.
I think the corsair is one of the few that has the shaft right in the center. I think you would be fine to mount your engine upright. Im pretty sure Ive seen some corsairs with the engine mounted on its side.