Either a stopped up radiator, stuck thermostat will cause overheating. I'm not familiar with 261 water pumps, but impellers can fall off most water pumps. Did you have the radiator cleaned? What is the history of the engine? Do you know that it ever ran without getting hot. If engines sit around a long time, cooling passages can clog up with rust or dirt. Did you buy the vehicle with the engine in it or did you buy an engine and install it?
