[skogs]

You will have to remove the stud-bolts from the stock header. Either that or remove the front-pipe. If you just remove the nuts you wont be able to maneuver the header out of the car.

Use a stud-remover tool, or make your own by tightening two nuts against eachother on the stud.

Also, you might want to consider wrapping the header if its stainless. Stainless header on stock exhaust can sound a bit farty, it does so on mine anyway. So i'm having it wrapped next year.