you can mount a 98 to 00 bumper on an 01-03 (maybe higher, idk) and vice versa. As proof they both mount up the same way, here's a 99 with an 03 bumper.
Four bolts holding the front bumper on, 3/4 or 19mm. You'll definately want half inch drive tools, esspecially a nice long breaker bar to break 'em loose. Have a friend to help you as these bumpers are very unwieldy to handle alone.
You can find all the parts you'll need on rockauto and ebay easily. the bumper itself will probably be cheaper on ebay than it will be on rockauto. If you find yourself needing bolts for the brackets to fix the bumper to the frame, use four grade 8 half inch bolts, 1-1/2 inches to 2 inches with either lock nuts or lock washers. Bonus points if the bolts and washers are plated or stainless steel. Defiantly don't cheap out on the bolts, though.
Also, good luck with the lower valance. No, seriously, good luck. Those things are an absolute pain to install and you'll probably end up ruining it like I did. Definitely try to get the bumper with a valance already on it.
Also know that if your Ranger has J style towing hooks like mine does, the 98 to 00 bumper will need to be dropped considerably for the hooks to clear, which won't look right. If you don't have J hooks then no problem. Another option is to leave the valance off entirely and go 'baja' style if you're so inclined.
95-00 Explorer bumpers will also mount up to the Ranger's frame in the same way that the Ranger bumpers do, but be warned. The brackets WILL need to be modified for it to slide all the way up to the headlights and grille, due to the design differences between the Ranger and Explorer. More work, but still an option if you're so inclined.
If explorer parts interest you, you can do an entire front clip swap (headlights, grille etc) from an explorer, but that's another tangent and a lot of work to do that requires a lot of skill to pull off.