Help with Cooling Issue Please

Ok, my 66 dart went from a 273 v8 to a 360 magnum..I used the 273 water pump etc, so I could keep the existing radiator. Just got the car back, on the highway it runs about 190 degrees...if your in stop and go traffic, it runs up to 210 degrees quickly...that being said, what should I do to make it run cooler?? I am attaching a pic.. I think it has a 22" radiator measurement from bolt hole to bolt hole is about 26" help please, Thanks!