Runing Hot, '64 Barracuda

I have a '64 Barracuda that has a 318 swap. We bought the car with the engine in it already, so I am not sure on a lot of the components. The engine seems to run a bit hot, but the fan does kick in. I am wondering if I need to install a larger or aftermarket radiator because of the larger motor or do I just install a colder thermostat? Or are there other options or ideas that I am not thinking of. Thanks in advance.