Explorer Interchange
Engine: The basic SOHC 4.0 interchanges between all years, and you can even swap in Mustang motors with a little fiddling so I've read. The intake and wiring must be kept in the recipient vehicle and the engine wired up to match that vehicle.
Transmission: Not sure, there are several varieties of the trans, but most likely 4WD models '97 to '01 only. 5R55E is what you should have, next series used 5R55S, don't know the difference but you can bet it's enough to fubar a swap.
Rear axle: '97-'01, possibly earlier models as well.
Many of these go to the crusher due to the failure of the SOHC motor, so if yours is in good shape that will probably be an easy sell. Transmissions are trouble as well, again, an easy sell. And believe it or not, the rear axles become howlers on a semi-regular basis, so again, someone shocked at the $1200+ tab to fix a howler will jump at yours for the much more reasonable amount you are thinking of selling it for.

Also, when you go to peddle that axle, be sure to advise on the gear ratio and if it is a limited slip. Selling points you know.
Good luck with it.
You could also just call a junkyard. Just ask, "Will that engine in that '03 (or whatever year you're interested in) you have interchange with my '01". They'll usually tell you what they have on their lot that you could use. The junkyards typically subscribe to Hollander Interchange
What you typically won't find is parts that will physically interchange but may not have the same part number. For example, lots of people put Mustang wheels on Rangers, but Hollander won't list that because the Mustang parts were never put on a Ranger. Also, most of the time you won't be told that you can put a Mustang engine in your Explorer but you'll have to change X and Y to make it work.









