It’s going to have the P.I. variant of the 2 valve SOHC 4.6L or 5.4L. Most likely the 5.4L (much more common in the Expedition than the 4.6L), It’s very, very common engine, not quite as ubiquitous in a recycler’s yard as a SBC, but pretty close. The OP should have no problems locating a used engine if he chooses to go that route