Project Wolf in Sheep's Clothing: 273 - > 408 Magnum Swap

I installed a/c and had to move the radiator back an inch. So I understand your issue. My car came with a/c so I found the stock rad on amazon. $150.00 less than Year One, same part #. runs at 180 @ 75mph with a/c on.
As for yours cooling at a normal temperature (180 or so) you just have see how it does when your done.