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Keep in mind some Ford 3.0L OHV engine are flex fuel (engine code "V") as opposed to regular gasoline (engine code "U"). They use different-size fuel injectors.
Also, apparently sometime after '99, Ford added a knock sensor.
Some people say that it's better not to use a 3.0L from a Taurus or other application wherein the engine is mounted transversely. See: http://rogueperformance.com/vulcanFAQ.html
The front wheel drive version of this motor is not compatible at all so don't even bother, just get a 3.0 from another Ranger of the same vintage(junkyards usaully have a cross reference to know what will plug in, and swap it in. DO NOT use any wiring that comes with the donor motor, strip it all off and use only what originally came in your truck.
I did exactly this with out '04 and it was pretty much a weekend project.
The RWD and FWD engines are the same, with different head gaskets to direct the coolant flow properly for each application. The sensors will vary with vintage and application.
The easiest to do, not requiring removal of the intake & cylinder heads is to find one of the same year with the same emissions spec, or at least the same emissions equipment.
As noted some have knock sensors, some have distributors, some have cam sensors and all have 6 cylinders. You can get flat tappet and roller tappet versions.
OTOH, you might find a low mileage engine from a FWD, and then it might be worth the extra time and materials to do the gasket swap. Depends on availability and what 'sells' in your locale. The DOHC engine from the Taurus/Sable will fit into the Escape/Mariner/Tribute trio, with a few changes, and is available for a LOT less, even though it is the same basic engine. Not that it would fit into a Ranger...
tom