The trouble you will find is that modern rear sets for disc brakes simply don't have the parts needed for ready adaptation to a drum set up. That means you will have to make (or adapt from other drum brake rear set parts) all the bits in between. This is the case for most "universal" set ups as well because even though most bikes with drum brakes have nearly identical set ups, the specific small differences make the connecting parts too various.
Mostly this means retaining the original factory pivot and crank arm that pulls the long rod that actuates the brake. This is far more important than is evident to most people. The reason is that the location of the joint where the crank arm pulls on the rod is very critical. That joint must be as close to the swingarm pivot as possible and along a line drawn between the swing arm pivot and the rear axle. Even a small deviation will result is noticeable oscillation at the pedal when braking over bumps. Actually, at the stock location there is still oscillation, but it is so minor it is not a problem. Remember, I'm talking about the pull rod-crank arm connection, not the pivot for the brake pedal. That pivot can only be in two places: Either directly above or directly below the pull rod joint. (or very nearly so) So you need to leave all that intact and connect up your new pedal to a new crank arm attached where the old pedal was attached. This is invariably splined, so a ready solution is to alter the pedal into a new crank arm. This can be connected with a rod and heim joints (spherical rod ends) and it is vastly better to load this arm in tension than compression but if it is robust enough compression is ok.
All these problems can be overcome with a cable system, but the cable must be pretty stout. They are pretty simple, but finding/making proper parts can be a lot of trouble. And the routing of course is very important as the suspension moves a fair distance and often violently. But cables are completely immune to the kinematics of the suspension and are far easier to engineer. The other thing is that once you get all the cable bits sorted out, you can simply relocate the whole works anywhere you like and only have to make new mounting points and possibly a new cable if the length can't work. Very often moving the pegs a bit up or down, or more to the front or back has huge benefits, and this easy relocation capability can be a huge asset. Such a system also migrates to another completely different bike pretty easily for what it's worth.
Here is a cable set up on a bike I did a while back: