I might not be much of a help, but I can tell you Long Tube Headers on your 4V will gain some power, there a pain though.
Shorty headers arent worth the trouble. If your going to go with an X-Pipe, go Bassini, of course they arent cheap, but I've heard only good things about them and I guy I know with a 99 Cobra said his went on flawlessly, along wiht the Bassini cat-back.
If you decide to go the H-pipe route, Flo-Tech is cheap, but it was a head ache to put on. Thats the only brand I have ever had any hands on experience with when it comes to H-pipes.
WIth a Cobra, I'd go with an X-pipe because the Cobra loves to rev.
------------------
64 1/2 "D" code Red Mustang Coupe. 289, C4, Mallory duel point. Ported & Polished 65 heads shaved .01 with 351 valves, 11:1 comp, 1.7:1 rockers, blue wolverine lumpy cam, modified 4100 Hipo 4 barrel. GT Apperance pkg. And to many others to list
2000 Perf Red Mustang GT. 5spd. BBK Underdrive pulleys, Flotech off-road H pipe. Hurst T-Handle, 40 series Flowmasters, Steeda Tri-Ax
64 1/2 red 6cyl coupe.
