I would just mount sideways and use the pitts muffler myself. This will put the exhaust straight down below the plane. Almost completly eliminates having any fuel spray to clean off the plane. You can also look at a slight downward angle mounting which will use your standard muffler and still put the exhaust below the plane. You may have to shave a part of the fuselage to make the muffler clear depending on the particular plane. Either method doesn't seem to bother the engine where as inverted running with a 2 stroke can be a real pain. [8D]