Designing a tuned pipe muffler is a tough proposition. It involves creating a pressure wave that amplifies itself. The length of the pipe is adjusted based on the timing for that wave. Because of all that, most tuned mufflers wind up being pipes or tubes. They need the length to "catch the wave".

So don't look for pitts mufflers that work like tuned pipes. The requirement to keep all the muffler within the cowling blows their chances of creating the amplification.