When you say "overheats" are you referring to what the rad is doing or what the temperature gauge is showing you. If it's the temperature gauge climbing toward the H mark, take the car for a drive and see if the gauge comes back to the middle mark. If it does, your '50 is behaving properly. If not, check for a collapsed rad hose. If you're still having a problem, go back over the rad, water pump and thermostat to ensure they are operating properly. Even "new" ones can be bad.