master cylinder shot?

One end of the pedal rod has a rubber ring on it that compresses enough to land in a groove in the back of the master cylinder. So... disconnect neg batt cable so brake lamps are not kept on. Remove the bolt attaching the rod to pedal arm ( under the dash ). Then 2 line fittings and 2 nuts ( under the hood ) and its out. Once its at the workbench, You're going to see a tiny metal finger with screw on the backside. This is the only thing holding the spool valve/spring/guts in the master cylinder. So try to separate rod from master cylinder without pulling the master cylinder apart. Or pull it apart and spill remaining fluid all over. Your call.
All this and much more is found in factory service manuals. Many of those are free downloads at MYmopar.com . If you intend to do these services yourself, that manual is your best tool.
As for which master cylinder to buy... disc/drum units have larger reservoirs, holds enough fluid for calipers. Drum/drum does not.