John,
The Ultraflows are 6" in diameter and the body is 16".
The lengths were determined to follow the profile of the chassis side. I use a "trombone" on the side under the clams to get that much length.
You may be able to find a longer muffler that fits just along side the seating side of the chassis.
You do not want to use a supertrap. To get the BDA quiet enough, it was so choked that the back pressure caused the engine to stop running after about 30 seconds and this was using the larger supertrap.
The other area that has to be addressed is the intake noise. If you can see into the intakes, so can the sound meter. It was quite a bit of work to make my air intake using 1/8" alloy, but it takes that side to reduce the booming that occurs with thin materials.
Call me if you want to talk, We have worked hard to meet the restrictions at the stadium. Even the Emod champ, Jeff Kiesel had to make many modifications to meet the requirements. 93db@50ft means that you hardly hear the noise at the edge of the stadium.
Wayne 619-444-0840