Downflow VS Crossflow Radiators

What makes a crossflow better is that it is usually bigger. In the case of your vehicle, to put a crossflow in the stock location would not gain any size. Therefore it would not be any better. If you wanted to shoehorn in a wider crossflow, then you'd have more volume and therefore better cooling. However, most owners don't want nor need to do that. The best way for an A body owner to get increased capacity is to increase the thickness of the core to add more volume. Mopars never had 4 row copper/brass units originally. So your upgrade would need to be (in ascending order of capacity) from a company like US Radiator with a 4 row copper brass unit or if you wanted to go aluminum, you want a 'big' 2 row radiator of dual 1" or 1 1/4" tubes for maximum capacity. Any other upgrade options would likely be a lateral move for you and therefore you'd be better off staying with the original 3 row (or restored version) that was in there to start with.