An OBD 1 would have been easier, but I swapped a 4.0 SOHC and 5R55E into a '94 Explorer. You will need the harness, ECM, and under hood fuse box.
I used the Ford EVTM (wiring diagram) books for both the '94, and in my case, '97 Explorers. I found them on Ebay. I recently replaced the 2.9 and A4LD in my 86 Bronco II with a '94 4.0, and M5OD from an Explorer.I used the Explorer harness, ECM, under hood fuse box, and accessories, including the A/C.