The explorer discs have the best of both worlds. Discs are better for stopping, drums are better for holding. So the Explorer rotors have a small drum brake integrated into them as the parking brake.
I knew that Currie had a kit for them, but I don't know much more than that. You might be able to just by the caliper bracket from them and source your own calipers and rotors, but you'd have to redrill the rotors to 5 on 5.5. Also, I had heard that Currie had quit promoting this setup as their supplies of the Explorer parts had dried up. That may be hearsay though.
Dusty