Ma Mopar probally decided to change the inlet and outlet sizes of the hoses to make sure the coolant routing on the hoses was done correctly at the factory and later on when the vechicles got older and needed the hoses changed. I'm not sure exactly if it was 1969, 1970 or 1971 when the factory did away with the same sizes hoses for the inlet and outlet on the ehaters, all those before the change had the same sizes hoses for both in and out The air condition vechicle had those heater control valves but the non air vechicles didn't and it wasn't hard to mix thoses hoses up on any of the early motors with the hoses sizes and inlet and outlet fittings the same sizes