[SFfiredog]

The Ford Motorsport GT-40 head (not to be confused with the original GT-40 heads used on the LeMans GT-40s of the '60s)
is iron and offered over the counter and was later used on the '93 and up Mustang Cobras and '93 to -95 Lightning pick-ups.
The GT-40 P was original issue on 5.0 Explorers and while the same specs as the earlier GT-40 head, the spark plugs were relocated in the combustion chamber for better performance and emissions. THe GT-40 P head requires different exhaust headers than the earlier GT-40 because of the relocated spark plug.
The GT-40 X head is aluminum and has slightly larger valves the the iron GT-40 heads and is the standard aluminum head for Ford'scrate motors.
All GT-40 heads offer excellent low valve lift flow characteristics and are very good for a mild to somewhat hot street motor and offer good value for the money.
--Mike