everything 87 up had e7s from the factory.
93 cobras, lightning pickups, and some explorers for a few years had the regular GT-40s
later year explorers had the gt-40 Ps which are the best factory head.
they have a smaller exhaus valve. but a totally different port design but the P heads flow better than gt-40.
the alum gt40s are different, they are aftermarket and flow better. IIRC the X gt40s arent much more than the regular iron gt40s and the Y gt40s are the better alum gt40s