You could mount it sideways and use a pitts style muffler, or upright, but both methods would take away from the looks of the plane and could cause fuel draw problems due to the tank location. The only way to use the cowl is to go inverted. I cut my lower cowl completely away to allow for the 2 stroke, and that makes it great for easy removal. I don't have to remove the prop to get it off. Don't sweat the inverted engine. If you have a proven engine that runs good otherwise, I'm sure it will run fine inverted. I don't even need to use the starter motor to get mine going, and it runs perfect.