I checked the flange already, and the thickness, there is a small piece welded to each of the center bolt holes to compensate for the thickness of cast iron. bolts line up with the head perfectly. The ports need a little cleaning, they left them slightly less than desireable... some deepish grinder marks and such. I'll definitely try it in the gt before I send it off. I had to do this with my Nova headers too since I moved the engine back a couple of inches from its stock location in that car.