I don’t know the history of your truck, or what you have done on it, but as old as it is if you don’t know what has been done to the brakes, I would recommend replacing all parts that are in contact with brake fluid. Lines, wheel cylinders and master cylinder. If it has sat for any length of time, you will probably find rust in all of those components. Dpending on the severity of the rust, a simple overhaul of the cylinders will not work and you will have leaks. Drum brakes are not as good as disc, but they should work just fine in normal use.
Lee.
