Overcharging 68Dart...need some short fused help (pun intended:)

Looking down the road see if there is anyone in your area who fixes radiators.
Since you're not in a jam (because you've installed the aluminim) then get it fixed right. If it needs a new core or header, those are expensive.
If no one local can do it, or can get the parts, then call Bob at Glen-Ray Radiators. He'll fix your old one and replace any components that need it. Budget around 500. It may be less since yours would be a repair and the number I've giving you is ballpark for a custom built one.

Then you can sell the aluminum radiator and electric fan and recoupe some of the cost