If you go with that radiator could you let us know if it works? I also have a 1973 wagon. I had the radiator repaired by a local shop about a year ago. It's still holding, but I don't know for how long. I live in the Phoenix, AZ area, where it is HOT, and does not freeze during the winter. I am using a 160 degree thermostat, distilled water in the cooling system, and running it with the radiator cap loosened to a half turn so it does not build up pressure. It runs fine that way, and even in the middle of the summer, when it is 115+ degrees, the temperature of the water does not get close to 212 degrees. Yes, it takes it longer to warm up, but it never really gets cold here, and the car does not have a heater. I am afraid that pressurizing the cooling system might cause it to start leaking again.
Oh, and can I ask where you got the 14" wheels? Several years ago I saw some 14" chrome smoothies from Summit Racing with a Pinto bolt pattern, but they are not there anymore.