Someone will correct me if I'm mistaken, but as I remember, the 96 & 97 Explorers had regular GT40 irons, the 98-01 Explorers had the GT40P's. (and 2002+ are 4.6L modulars, not 302's).
97 was the transition year, so some early 97s had the Gt40 heads and later they had the GT40P heads. The GT40 heads have three vertical bars cast into the front ot the head and the GT40P heads have four. Gt40 heads have "GT" cast into the head near the Passenger front header bolt and the GT40P heads have "GTP" in that same position.