When you are looking for a muffler/resonator, I would look for the 18" Magnaflow and I believe the 12" Vibrant. Maybe do the Magnaflow first to see if you like it without the resonator, and add the resonator later if you don't.
Double-check with Sonic, but I'm pretty sure that those are the two he used for his side exhaust. They are both straight-through design and we double-checked with both companies about their flow ratings. He also has some video and driving impressions
Sent from my stupid phone, please dismiss my illiteracy