GTp heads do not have passages for the smog pump, so if you need to hook up the plumbing to your smog system they will not accommodate it. I drilled and tapped a hole on the back of the head so I could install the smog plumbing to pass the visual inspection. I run a belt that bypasses the pump and only install the correct belt to get the car inspected.
I was able to run the aftermarket headers my car came with. (unknown brand) I had to dimple the #8 tube a little and run 90 degree plug wires. I will have to remove the drivers side header to change my plugs though. Ford Racing makes shorty headers that work on the GTp's. So, when I get around to changing the plugs I will probably buy some new headers.
If you are running a larger cam I recommend changing the valve springs.
GTp heads are basically GT 40 heads with smaller combustion chambers and of course the angled plugs.
The intakes changed after 97 and the newer ones do not have the internal EGR passage. So, to make your EGR function you will need to get a '97 or older intake. You will also have to drill and tap a hole for the IAT sensor. The '97 and older intakes have the casting for the IAT in the same place as the original 5.0 intake, the '98 and newer intakes do not.
My engine is a .030 over 5.0 with the GTp heads off of a 2000 Mountaineer. The bowls have been blended and the exhaust ports smoothed out a little and the Intakes were gasket matched, '97 Elplorer intake with the lower also port matched and "worked", B303 cam, Trickflow valve springs, 24lb injectors, 70mm Throttle body and EGR spacer, a cold air kit that puts the filter in the fender and a Mass-Flo 73mm mass air sensor calibrated for the 24lb injectors. Haven't had it dyno'd yet, but I'm guessing about 250 to 275hp.