I would buy a '02 Ranger with as many of the features as you can get to match - air, cruise, manual, etc.
In addition to the engine and transmission, wiring and ecu, there's things like PATS, which leads to door locks and tachometer for which you'll want the entire display; that you would want.
It's very much the converse of the 5.0 - down 2 cylinders rather than up. And 5.0 includes transmission/transfer case work - a 135x never bolts direct to AODE or M5OD-R2. Effort/cost being more/less equal...