I know that the '99-'04 stang gt heads are the PI heads but did Ford place the same head on any other vehicle prior to '99? In my area it would be cheaper for me to buy a jy engine than t oorder a set of heads. Prob w/ that is that there are none to be had.
No they didn't. The first crown vics, town cars, etc... that saw PI heads were 2001. You may have luck at the junkyard finding them in taxi's with high mileage and really even they are in better shape than most Mustang PI heads as they are run 24/7 and get oil changes practically weekly. The main thing to look at is the cam journals for wear.