Other models work for the swap, just more usually more wiring work involved unless you go with a carb'd 302. The 98-2000 4x4 automatic Rangers work best for the swap because you can find a drivetrain out of an Explorer or Mountaineer that will nearly drop in. For the most part, the wiring harness hooks right up (I think I had to splice something like 5 wires) and the anti-theft stuff will swap right in so it's plug and play (you'll need the computer, PATS module, ignition cylinder and keys out of the donor truck). Driveshafts match up so it makes for an easy swap. But like I said, there's a narrow window of what Rangers work and what Explorer/Mountaineers work for the swap. Anything outside of that, and you're back into splicing wires and making things work. Of course, there are some decent write-ups about doing it on older and newer trucks too in the tech library.
When I put together the one I did, my dad had bought a 2000 Ranger, extended cab, 4x4, auto, fully loaded, but with a bad 4.0L. We were going to replace the 4.0L, but then he stumbled across a deal on a Mountaineer of the right year that had the 302... so... yea... father/son project that resulted in an awesome little toy for us to drive. That is, until some jerk ran a red light and totaled it while I was driving and messed up my hip. Frame is bent like a banana. I'd like to have one of those again someday though. Real shame, it was a beautiful truck.