if its down where u cant get a nut on it. You might want to try the easy out.

The trick is using a very small drill bit to get the hole started good and center and slowly moving up sizes. It also helps to try small easy outs and going to bigger easy outs

It might b pretty hard with the engine in the car

 

well i forgot what its called but sears has a tool set that you hammer over the stud that cuts into the thread really tight. the size of the tool should as close to the size of the stud as possible and then with a ratcheting wrench with a pass through that the tool has crank that baby out.

my step dad is going to help me figure this out when he gets back on the 17th and if all else fails i'll try the tool sears has and if that dont work i'll just break down and start calling shops that'll be able to do it.

 

i used a combo of heat, pb, and bolt extractors from sears. I did have to re-tap the hole too.

 

Well it may be a little late,But What "should have been done" (been there) is to get a Tap and die set and Redo the thread on the Stud.Then take a grinder and "skim" a little off the Area around the Outside Hole of the header to make is a little Thinner than the Original thickness of the Exhaust flange.You could have also Made the Nut a bit Smaller by Shaving the nut down too,to give you a "little extra" Thread..NOW?..I guess the option is to Get Heat to the housing/hole area and the Stud itself, to allow the heat to penetrate it enough to let you Take it off with Either Vice grips or whatever..Sorry to hear things didn't go your way though.I have had the Same "luck"!.But,it Happens with 21 year old cars..Cheers,STYX.