I am in the process of installing a set of MAC longtube headers on my '01 GT. Called around to some shops in the philly area the average quote was around $550-$650 for the labor. Thus I decided to do the install myself, I am not going to lie it is a real pain, just because of all the little steps involved in a tight area. It is still pretty much a straight forward install just tight room to work in. I did not have to remove the k-member to get them in like some people suggested, it just took a little longer to get them in. You will also have to either purchase O2 sensor extensions or make your own extensions for the front O2 sensors if you go with long tube headers. Also do not buy the exhaust manifold gaskets from ford, you can get fel-pro gaskets that are about $20-30 cheaper than ford and are of better quality. Also you will have to replace the stock h-pipe assembly with with an after-market one designed for long-tube headers. I chose the MAC Prochamber due to good results with previous cars.