The Ford 8.8" rear diff's on all Gen II Explorers (2 doors, 4 doors, Sport Tracs an, Mountaineers) other than gear ratio, are all the same unit. IDK why Ford decided to put rear drums on the 2001-2002 Sport Trac, but the disc brake parts from another Explorer will bolt right on in place of the drum parts. I know this is so because I took a 4 door Explorer disc rear diff, converted it to drum and swapped it into my '01 Sport Trac. No modifications to the diff were required.
Here's the rub... disc and drum brakes require a different volume of pressurized fluid to work correctly. Usually the master cylinders are different, the
proportioning valves are different an the rear brake lines require a residual valve to prevent fluid pressure from draining back toward the master cyl. Disc brake calipers require a little bit of residual line pressure (around 10 psi) to work correctly. Some here will say they've converted their drum brakes to disc brakes without making any changes, other than rear flex lines and perhaps the
parking brake cables, to their drum system and that their rear disc's work fine. These people don't know what they're talking about. Don't' believe me? Contact someone like Wilwood or SBC and ask their tech experts. Consider the difference in fluid volume between a drum brake tiny wheel cylinder and a disc brake caliper. Without having residual valves in the system disc brake pads tend to back off the rotor slightly (especially if rotors are true) and will cause a low/lower pedal that requires an extra pump when braking.
What's wrong with having rear drums? Your rear brakes only provide 20-25% of your vehicle's braking power and drums can easily handle that. Don't get me wrong there are benefits to disc brakes over drum brakes. Ease of maintenance, more consistent braking and less issue with moister.
As long as we're on the subject of brake safety, another thing that drives me crazy is people who insist that home plumbing compression fittings are okay to use to repair your brake system and that they've done it for years w/out any problem. This is just stupid and unsafe. Consider that a compression fitting used in a home's water system only has to withstand around 60 PSI and that In an emergency braking situation you brake line pressure can be 1,200 psi.
