PI heads are the cylinder heads that ford switched to for the 99-04 mustang GTs. they are also found on F150s and 01+ panther chassis cars. they have a square inlet port with larger valves and a smaller combustion chamber. the PI intake is the intake made to match the airflow characteristics of the PI heads. i got my heads used for $170 on Ebay, but you can buy them new for about $400 a piece from various places. the intake is about $200. on a 96-98 GT there is a 50-70 hp increase from switching to the PI heads and intake. however the compression ratio is increased to about 10.5:1 so using a blower is almost out of hte question. the camshafts used in the PI heads are also different.
when you order the PI heads you get the PI cams with them. all you need to install them are a complete set of tools, the heads, intake, gaskets and new headbolts.