I recall on my 63 valiant, it had 2 different hoses, 1/2" and 5/8". Also, I just rechecked, at the engine I have 5/8" out of the water pump and 1/2" hose off the thermostat area.
I think someone has change something at some point. The standard heater hose sizes are 5/8 and 3/4. Always have been. I don't know what else to tell you.
