Best cold case/ summit for a 71 duster.

I assume you're speaking about an electric fan. Be advised, in order to achieve proper cooling, you need one that will move around 4000 CFM of air. Those fans AIN'T cheap. So, if you get 100 buck electric fan, just know it probably ain't gonna work. Also for radiator, I recommend a Griffin exact fit two row with the largest tube size you can get. They will probably be either 1.25" or 1.5" tubes. Get the 1.5" if it's available.