Jack,
If you haven't already, read
Chapter 5 of the 1948-51 Shop Manual as it applies to your 1 Ton Huck brakes.
There are removable plugs (could be metal or rubber) near top back side of the rear backing plates that you must remove to get a flat bent brake adjuster tool into the inner drum area and back off both adjusting wheel caps on the wheel cylinder. See Figures 2, 5 & 25 in Chapter 5 for pictures that show the wheel cylinder and adjusters to know where to look on your truck.
You will need to back those off to release the brake shoes away from the drums. If the shoes haven't moved in a substantial time period, you may need to rap on the sides of the drum to cause the shoes to free up from the drum, then proceed with drum removal per the instructions in the Shop Manual.
Before all of this though, make sure you have done what you can to release the parking brake mechanism. You may even need to disconnect the cable clevis on the side that you think is seized up to free up the cable and in drum mechanism.
Let us know how it works out.
Dan
