to be honest, you are better off with the regular heads. The P heads will give u very little gain. Besides, if u buy the P heads, You will need to buy the headers that go with it, i believe mac and ford racing sells them. but its in the 300 price range. and they are shorties. or you can look for longtubes that have good spacing so the spark plugs will clear (which must be 90 degree boots). the P's are a hassle IMO. i would stick to gt40's.
yeah the combustion chamber is different which is where the extra power is gained from. but idk, if he only has one hed and nothig else, it isnt worth it. look for regular gt40's in the explorers or mountaineers earlier than 97.
like i said, it does make extra power, but its alot more of a hassle. ive seen the flow charts, its not too much of a big deal. gives you some thing like 10-15 hp.
Our P headed car runs strong... they are a good budget head.