Napa PN = 600-1918 or it might be -1819. Youll know it when you see it because the package will say FORD or GM or what not. Off topic, i bought a stud kit for my 98 but the studs were too small to fit the flange. Dont know whats up with that. I just put the stockers back in. Surely the 98 GT Headers arnt different than 99+ or 97-? I dunno. Interesting to think about though. Good Luck.
Brian
EDIT: Should be your drivers side flange. The kit comes with 2 studs and 3 nuts. One of the nuts is used double nut the stud and tighten the stud into the flange. At least thats what i reasoned. Good luck!
With my xpipe setup a while back I had the problem with the pass side and we replaced all 4 studs then, maybe 2 years ago. Do you think they need to be changed again?
Well, that stud kit can be for either. And im not sure you need to change them because studs should last the life of the car. Have you developed a leak? Perhaps you just need to tighten up the nuts on the studs? But anyhoo i've only heard of it being used for prochambers. Some how the shouldered studs of the stockers wont allow the midpipe to be fully tightend up to the drivers side exhaust manifold. Personally, on my 98, i didnt see how this was possible because the shoulders on the studs sit so low against the flange on the manifold, and because its a ball and socket flange, one would have to tighten the poo out of it to get the nut to bottom out against the shoulders on the studs. I dunno. Ill give you a bump to get you back up to the top. Hopefully someone who has encountered the problem will be able to give you more info. I just telling you what i've seen on my 98, although it appears i have gotten the stepchild of mustangs. Good Luck