To answer a couple of your questions, this truck was a firetruck and I removed the pumper body. My goal is to have a platform bed on it. I have a woodworking business and the truck will be used to transport lumber ands supplies. My guess is that this truck will never see even half the weight its rated for. The tires need to be replaced and I am going to move to tubeless, centerless rims. If everyone would have said to get rid of the old brake system, I would have started looking for and older kodiak or C70 type truck to harvest the axles and wheels. I have been quoted $400 each to replace each wheel and tire and that was for retreads. I figured I could find a tired old kodiak or topkick with modern wheels and tires and it may even have the bed I need also for only a little more money than I will be paying for the new tires and wheels.
Anyway. It looks like there is no reason to worry about the old brake system as long as I keep them serviced. Thanks for the advice. I am ready to move on to others areas of this truck that are more satisfying than brakes and tires,