Going through a turbo will take quite a bit off the 'edge' as will a long straight pipe. You might consider getting a 'Y' to put near the back and shoot exhaust out both sides--that will also help some.
The mufflers on the semis I drive at work have all broken at the bottom where the pipe goes into the muffler. There was nothing wrong with the rest of the muffler. I took a plasma cutter and cut a circle slightly larger than the inlet pipe. This allowed me to have enough room to reach in with the plasma tip and cut out the perforated metal inlet screen inside the muffler. I then welded in a new piece of inlet pipe and made an adapter 'donut' to fit the new pipe to the larger hole I made in the muffler. This modified muffler has a little more rumble than the stock muffler but it will still take the edge off the Jakes when I use them. Backpressure is dramatically reduced. One truck I drive has single exhaust and it had a small leak on the pipe near the elbow going into the bottom of the muffler. After I modified the muffler the leak is no longer noticable.
Most trucking companies would not go to the trouble I did and you might be able to get a 'freebie' muffler to modify. You could also cut the muffler to whatever length you desire.
Just a thought...
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