The original radiators dissipate heat better than aluminum. These engines and radiators were designed to work together, quit well.
I agree with Russ. I don't see an advantage of the aluminum ones. If you have over heating issues, it is probably elsewhere.. or just a clogged radiator. With that said, there are others that have installed the aluminum ones with no issues and do give you a modern look. Perhaps they can chime in if you are intent on aluminum.