[vince1]

I'd change a rad before pulling an engine.

I changed my 250 to a 350 and the fan is now quite a ways back without a shroud. I put a temp gauge in to supplement the cold/overheat light and am surprised it doesn't overheat.

You said you checked the water pump so the impeller must be intact. I had a car where the plastic impeller broke apart and the engine would overheat. Also, make sure it is turning the right way. I don't know if in your case it is a possibility but on some cars that also use serpentine belts an incorrect pump could turn in the opposite direction.