You can get them from a mid 97 and up explorer. 96 and early 97s had regular gt 40s.
Personally I would change out the valve springs and have a valve job done on them. I don't know if the valve springs will work with the stock HO cam but I know that if you are going to change cams then you will need to change valve springs so why not do it now and save some hassle later on down the roal. I went with the trickflow kit for cast iron heads from summit.