That radiator looks to be in excellent condition. I wouldn't hesitate to grab a soldering iron (one of the ones with a big chunk of copper at the end) and solder up those cracks. I might drill the ends of the upper one, but cleaning the area and soldering should make it leak-free. Easy enough to test for leaks by installing the cap, laying it face down, attaching a couple of foot long pieces of radiator hose and filling it with water. Or getting a couple test plugs and applying about 5 psi of air and use some soap solutions to check for bubbles.
