My experience is that if you replace the ENTIRE brake system on your old truck, it will be the last time you will touch for another 50 years or so.
DOT3 fluid is hydroscopic which means it will draw in moisture if it is exposed to it. Once you develop a leak, it's working in two directions; letting fluid out and moisture in. That in turn sets the old tin worm to work and that in turn starts rotting lines from the inside out. A brake line can be all painted up and look great and blow out an elbow at the first stop sign.
Replace the whole enchilada (wheel cylinders, master cylinder, lines) now if you do anything and you'll never have to deal with brakes again in all likelihood. Shoes can wait if they are ok.
