Don't know if this will help, but my ol' man had a '49 Pontiac sedan and a '53 Chevy sedan with that kind of setup.
There was a large drum on the driveshaft behind the transmission, with some kind of external brake shoes that wrapped around it.
I don't know how many years GM had it, but his '57 Pontiac had a "normal" rear brake drum setup.
Maybe try and find an old basket-case Pontiac or Chevy sedan, and see if the parts will fit on an AD truck.
Just a thought.
