You'll actually want a muffler with a 2" intake/outlet for the Bonnevilles with the dual exhaust. I'm not sure what it is if you have single exhaust. I do have Borla PRO XS mufflers on my Aurora, but like mentioned, it'll sound different than what a Bonneville will. On my supercharged Riviera I also had Borla but the Turbo series instad of the PRO XS and it was quite a bit deeper sounding, but it was somewhat raspy and popped a lot.
If I had to do over again, I would probably have gone with the Turbo mufflers again. The sound is a bit deeper and not as loud as the PRO XS'* are. It could just be the engine themselves too. the 3.5 is smaller than the 3.8 obviously. hah. I like the refined sound tho.
here'* a clip of my exhaust the day I got the mufflers installed (after they break in they get deeper sounding.)
And from inside: