I mount engines depending upon the cowl and or exhaust exits. On my favorite sport flier, Sig SSE I origionaly had the engine upright and all of the fuel residue would enter around the removable canopy. This winter I cut the nose off and mounted the motor on its side and now the exhaust from the muffler will exit out the bottom of the plane, a lot cleaner for the wing joint and canopy.
The distance from center that the weight is displaced is so small it has little effect, if any in some cases. Mount the motor in any position that favors the airframe/engine combination and always ballance the airplane lateraly.
Blue Skies
