64 Dart GT Slant 6 Electric Fan Conversion

I recently purchased a Champion 3 core aluminum radiator for my 225 slant 6. I am looking for suggestions for converting to an electric fan. Which fan size would work best, and should the fan be mounted toward the front of the radiator or back? Do I need to tap into any sensors? And, what type of harness should I use? Should I wire the fan to engage when the key is turned on? And, if so, where should I tap into the voltage source? I was thinking that the ballast resistor would be ok, but maybe I am wrong. Perhaps I should mount an underhood fuse panel which taps into key only voltage?