There are many ways to swap Ranger rear drum brakes to discs if one is so inclined. Here is the conversion that I did on my 2003 several years ago. This combination works very well but it's not a simple bolt-on swap.
Before: factory 10" drums
After: SVO 11 1/4" vented rear discs
79~85 Eldorado/Riviera/Toronado rear caliper w/parking brake
84~86 Mustang SVO 11 1/4" vented rear rotor
94~04 Mustang GT front brake hose
Custom fabbed caliper bracket, splash shield and p-brake cable adapter.