I also bought my Flowmaster 2.5 kit from Summit. I've yet to start the engine but the kit is awesome. It comes with everything you need to do the install. You will need to weld the included header flange to the included reducer since you are running headers. Click on the 2nd link below and scroll to the bottom of the page to see the whole system laid out on the ground. What's nice is it attaches to the stock mounting locations on the Firebird and fits like a dream (even with the car lowered 1" in the rear and 2" in the front).