Slow, Driving Rustoration 1972 Dart

I was going to suggest an external cooler if you want to get by with what you have. They are relatively cheap and easy to install and you'd be back on the road in no time.

In my opinion, the car is almost fifty years old, and if it hasn't been replaced and you can afford it, I'd go with a new Spectra radiator. There is no reason for you to go with a three row Champion (which I did) for the level of driving that you're gonna be doing. Spectra makes a good product and you'll be happy with it. Get the part number from RockAuto and then search around the internet for a better price. Using a coupon from AutoZone or Advance can sometimes beat RA on big ticket items.