Like said above, it's never going to sound like a V8. At idle mine confuses a few people because it's very deep and raspy, but as soon as I rev everyone that even remotely knows about Mustangs can tell it's not a V8. For a relatively stock V6, headers aren't worth the money, as the stock ones are surprisingly efficient up to around 300+hp which I doubt your cousin will be making anytime soon. Also tell him not to touch the cats. Gutting the cats on a V6 mustang = instant honda civic sound. Trust me, I know. Keep the stock headers and cats, and have a custom catback welded up. I went with dual Flowmaster 40s and couldnt be happier.