In my over 50 years of auto experience, it has been my experience and advice to research whatever product you are going to use. In your 1950's vehicle with a 4 to 7 psi cooling system that runs at 170 degrees, use the old standard ethelyne glycol based Prestone or its equivalent. That also holds true for some newer years into the 60's and 70's. The new hybrid coolant technology is for the high pressure, high temp cooling systems that are basically sealed to atmosphere. My 1951 Frazer with it's low pressure, low temp cooling system has served wonderfully with old green Prestone. My 1954 Kaiser Darrin V8 cooling system, runs 16 psi and 195 degrees up to 210 degrees all day long for the last 5 years with no problems, but I have designed that cooling system (tube and fin radiator core and tube and fin heater core) to use the later HOAT or Hybrid Organic Additive Technology. The system is sealed and recovers any coolant expansion on it's own, and doesn't overheat because of the extra system pressure. Also, these latest organic coolants will grow mold and mildew on them if they are exposed to atmosphere and do not get hot enough. Organic being the reason. Stick with Prestone or its equivalent, drain it and flush it as required and you'll be good to go.
