I Have a 59 chevy and have the basic heater, one switch for the fan. There is an upgraded heater that functions like a modern heater in a car, that you can adjust the temp. There is a valve called a ranco valve. Your heater doesn't have that valve. That is probably what the shop is talking about. On the other hand they may be talking about a shut off valve, but that is not connected to the core , it is inline from the water pump to the heater core.
