Did you want to try to swap just the muffler? I was going to stop by the performance shop I use to get dimensions on some stuff to try this weekend. I'm sure they'll have some recommendations for a custom shop as well.
Hi Chad! Ya, that would be a very good start. The guy at Roush I last talked to, told me the Roush muffler had the same inlet/outlet sizes as stock. Actually, he said, "I think". According to him, there were no engineers at their desks he could ask.
It "appears" to be 2.5 in, and 3 out, straight in and out, just like the stock resonator, in fact, their muffler, and the stock resonator, are identical.
I've even thought of putting the stock system back on, minus the resonator.
But yepper, anything you could find out would be helpful. Thanks man!