You didn't mention what the temperature was when "the coolant is boiling out of the overflow tank."
I didn't see anywhere where you mentioned anything about the radiator cap. It may be releasing below 4 # of pressure, thus overloading your overflow tank making it appear to be "boiling out'"

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