I just picked up ~25 hp going from a TTI full 3" system w/ H-pipe to a 3.5" system with an X-pipe and dumps before the axle on my 493".

I've had good luck with the 4150 M1, but you might want a Dominator. Who is footing the bill at the gas station?

Faster, Faster until the thrill of speed overcomes the fear of death...

71 Swinger - slowly collecting dust/parts
66 Belv. II - just a streetcar
88 Mustang - turbo LS beater