Let's remember that a thermostat establishes the MINIMUM operating temperature of the engine- - - -the size and cleanliness of the radiator and the airflow through it controls the maximum temps. Ambient temperature of the surrounding air and the load the engine is pulling will have somewhat of an influence, but keeping things cool is mostly a function of how much heat the radiator moves from the coolant to the surrounding air. Copper is a much better heat conductor than aluminum, so it you choose to use a modern aluminum radiator, be sure to upsize it a little.
Jerry
