If you look at a PP fender liner, there is a rectangular hole towards the inside front part of the liner. That's a brake cooling duct.
You can see pictures here:
https://www.mustang7g.com/forums/th...rake-ducts-in-a-gt-5-0-pp.161925/post-3288182
Check the picture in post #18 in the link in the quote above of the end link for a non-PP GT - It appears to have the 3 threaded taps for the PP deflector already there.Its a different front underbody has 2 ducts. It also requires a controll arm to be changed out for the air deflector