Most of the time the idea is to have as small a frontal area as possible. Example, look at the profile on a p-51 Mustang. The spinner is at the top of the nose with an airscoop under it. If you mount it right side up
then most of the cylinder head sticks out the top. Upside down the head is enclosed but your muffler sticks
out the side. On it's side is the best compromise. The head may stick out a little but that helps cool it and you
have plenty of room under it for the muffler. In any case as long as the crankshaft centerline is lined
up with the fuse centerline the plane will fly the same. But why spoil the looks of your bird and give it
extra drag if you dont have to. later daveo