PI heads are called "performance improved" heads. They are from a 99+ Mustang GT and the PI swap you hear about includes, the heads, the intake manifold, and the cams. All of which come from a 99+ Mustang. 2002 I believe is the year with the aluminum crossover for the intake manifold so it wont crack and leak coolant all over like every other year. Might want to check into that. The cams, so seperately usually cost you about 100 bucks, the heads are around 300 and the intake manifold costs about 150. Alot of people will sell a PI swap for about 500-600 bucks. Good luck with everything!