If the car has the Shelby H/E brackets, its should fit. We just had a customer buy one for a Roush, I guess the S/C Roush's come with the Ford/Shelby brackets off the lot.
I'm going to correct Derek in regards to the bracket and mounting of the heat exchanger. The heat exchanger will bolt up to any 05+ GT/GT500 as it uses the 4 bumper mount bolts as a mounting point. That means that there's no brackets needed as they are built onto the heat exchanger already. Here's a picture of the the front bumper of our GT500. You can see the 4 bolts (2 on each side) that go through the metal bumper support. That is how it is on all S197 GT's and GT500's.
So the heat exchanger will bolt up. It's the routing of the hoses that you may need to modify a tad as the GT's saleen hose routing is slightly different then the GT500's hose routing. Here's a few images of a customer that installed the AFCO heat exchanger on his GT that has a Saleen kit on it. You can see what he had to do in order to get the hose routing to work.
Please let us know if you have any other questions.