I agree with Jim, you really can't be too careful. DOT3 brake fluid draws moisture bad and the brake lines (tubing) rust from the inside out. The bleeder screws are probably clogged. Remove each of them and clean out with a piece of wire. With bleeder out pump brake pedal and see if line is clogged. It would be best to pull all wheels and drums and inspect everything. The 50 3/4-ton I have now had been sitting up for maybe 20 years or more. Every wheel cylinder was frozen, corroded solid. I was able to disassemble each of them and rehab them, honing the cylinders and putting in new kits (rubber), and am in the process of replacing all the tubing and hoses. Your problem may not be that severe, but I recommend caution. Good luck.

Professional Novice