RE: Sideways or verical engine mount?
I would also add be sure to balance your plane laterally with all equip either installed or in place(in case you need to move anything around to get balance close befor adding additional weight)especially if you mount engine sideways.add weight to light wingtip.this will ensure that your plane flys true.also mounting sideways will allow installation of tuned pipe down bottom of fuse if ypu want later on.thx.