Some GMC's and Fords have a big cam bolt top and bottom on back plate. Loosen lock nut, adjust bolt/cam, tighten lock nut. There will be two seperate cyls to adjust on these. Get a brake spoon, much better than "driver" and has odd angles, easier to work with. Don't be suprised if you don't have to remove drum and work the adjusters some to get unrusted and moving. Adjust way out while drum's off, just enough to allow drum to slide back on.
Power booster will feel just like modern power brakes, plus when you let off, you should here a hiss or such at filter which is behind the rear seat in corner of cab. I drove mine w/out working booster for 5 years, just have to push a little harder on pedal. One day, the thing just started working after sitting half the winter, not sure why? Was much nicer to drive with a load after that, for sure.
