The swap from GT40 to GT40P heads occurred mid-year in 97. Early production Explorers and Mountaineers had the GT40 heads and egr set up just like the Mustangs. The late year production vehicles had the GT40P heads and no internal egr. The quick tip off is the egr valve - if it's present behind the manifold/throttle body, then you've got GT40 heads; if it's not, they're P's. I've got a friend with an early 97 Mountaineer engine tranny that's going in his 940 Volvo - he's got the GT40 set up. My brother just bought a late 97 Mountaineer for the engine/tranny swap into a 61 Falcon - his has the GT40P's.