I'll have to agree with KCMongo on this one. I run Fenton headers into a collector that goes into one 2 1/2 with one Flowmaster 40. It sounds bitchin'. It sounds completely different than if you had dual exhaust. A real throaty sound. Nobody knows it's a 6 until I pop the hood. The guy that built the exhaust for me used to build them for the inline Novas, back in the day.
Good luck.
