Need some electrical help with my ‘68 Plymouth Valiant 100

Detail exactly what the brakes do and don't do. Are these front disk or drums?
Drum brakes. I checked the brake fluid and the front half of the master cylinder os completely gone. So most likely something is wrong with the rear drums, or at least that’s what I assumed. I filled it with brake fluid and tried pumping the brakes to see if I could find leaking from the rears, but I couldn’t seem to find the leak.