There is nothing out there as a system for the Bonneville. You have to make your own. Our car is actually pretty easy. Just lob off the OEM mufflers right where they co into the mufflers then order some Magnaflow'*. The mufflers will slip onto the OEM plumbing. You'll then need to custom bend about a foot long piece about 60* to bring the tails straight out the back of the car (as our mufflers are mounted on an angle), then choose whatever tips you like.
I chose ones similar to these on each side;