Padre,
The muffler robs no power from the large Saitos. Don't be scared to put one on. My engine is mounted sideways/90 degrees. That is the way the Pitts muffler was designed. I believe they are coming out with one for the inverted setup also. It may be out already. Give slimline a call. It may however take a Loooooong time to get one from them. I found mine on shelves of other hobby shops. I had waited 6 months and no dice so I started looking elsewhere.