I've looked, can't seem to find any proven info on what spring would be best with an HO cam and P heads.
I've got to assemble a 5.0 for the Mounty, as mine is doing some strange things, and I've thought about either using an HO cam, or else the Wolverine cam, but IIRC it's too much for an auto trans, so I'm leaning to the HO cam. Rest of the engine will be stock, unless I can miraculously find some headers for a P motor IN an Exploder.
This will also pertain to my Tbird, as I have a set of P's to drop on it if I can ever get time to touch it.
These are a very popular spring for a lot of similar apps as long as you know how to set them up with the correct retainers, locks etc. All in all, they are almost a drop in.
http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=44
Those springs will work great. FRPP makes a set of offset retainers so they will have the correct installed height with stock valves.