Wow, that's a tough one. Looks like it already has rod-operated brakes, but those kind of rims don't lend themselves well to stopping quickly.
You'd need to replace your front fork to run disc, and ideally both hubs. You'd need to weld a bracket for rear disc.
Can you pull a brake pad and post a close-up? It's always possible you can find a suitable pad to replace what you have.