I use the carbide grinding burrs made for metal. I have a set of 3" and a couple of 6" for deeper spots. I use the cross hatch style (double cut) type most of the time but to remove a lot of material fast I use the single cut style. The "oval egg" shape is pretty useful for most everything but the "ball" style and the "rounded cylinder" style are pretty handy too. You can get them from most any tool seller (Snap On, Matco, etc) or online at industrial places like McMaster-Carr.com. Have fun and wear your safety glasses!
Maybe late for the party but with a straight 6 you don't want an true dual exhaust. Just smack a decent y pipe on there that doesn't choke like this one, and it'll rip!
