Lay off the crack .

First off, your KA24 doesn't have headers and it never will. Dual exhaust on your car would be pointless and heavy. There are a lot of aftermarket parts for 240sx and altimas out there, as well as hardbodys that may be compatible with your xterra. A nice, free flowing, 2" single exit exhaust would be nice. Or you could go nuts and turbo the thing. Still remember your pushing over 4000lbs with a 4 cylinder engine so don't expect a race car.