Hy Kyle M, welcome, we have a saying in the vehicle maintenance field "If it aint broke don't fix it". To start with lets get our terminology correct, what we are looking at in your picture is a rear Huck brake assembly, the item in the top center of the photograph is a wheel cylinder, not a master cylinder. The master cylinder is connected to the brake pedal and controls the performance of the individual wheel cylinders. If your wheel cylinders will adjust using the "bolt/spring" on the inboard side of the backing plate and there is no indication of brake fluid leakage, then I would check and reattach the brake return spring clean any dust/dirt out of the area and reinstall the brake drum. You are very lucky if your adjusters still function and things are not seized up. I would also suggest you purchase a maintenance manual which covers your year of truck. Good luck with your truck.
