James Duff, Skyjacker, and Superlift make the best TTB (Twin Traction Beam) lifts for '97 and older Ranger 4wd's. I have a 6" Superlift kit on my truck. I have had no problem with it. The way I listed the kits above are also the way they are in price (most --> least). The Superlift kit and the Skyjacker kits are basically the same thing. James Duff kits are expensive, but they are the best of the best as far as TTB kits go. However the closest to 4" kit that Duff has is the 3" kit. James Duff just released a 6" kit for the TTB Rangers, but it is out of this world in pricing.
I recommend the Superlift kit.
I also recommend going ahead and getting the 6" lift kit, it is only about $100 more than the 4" kit.