As far as the Ranger goes, 4wd and 2wd are built very differently in this area. With a 4x4 Ranger, the rotor is completely seperate from the hub and bearing assembly. The hub bearing assembly is also one piece in a 4x4 application.
4wd and 2wd front wheel bearing, rotor, and hub assemblies are set up totally different. On rockauto, you can purchase a bearing for each side, and it's literally just the bearing.
In contrast, rotors for a 2wd aren't built in the same way. I've never worked on a 2wd Ranger, so I can't say just how these parts go together, but that should at least shine a little light on your problem.