I have a feeling this is a stupid ? but I need to know. I'm looking at exhaust systems for an 2004 Mustang Mach I. The parts I'm looking at now are the catted SLP Loudmouth II's and I'm undecided on a x-pipe or a h-pipe. Now this is what I'm thinking... The SLP's have a cat and the headers have a cat. Do I need 2? Or do both have a catalatic converter? If they both have cats and I don't need two then can one of them be a Off-Road Pipe and it still be legal in NC?