Your new aluminum radiator is more efficient at cooling your engine than a stock radiator. You need a thermostat which does not go wide open at 160 degrees.
The temperature which a specific thermostat becomes wide open may vary from what temperature is stamped on it or what is written on the box it came in.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission