If you have a patient counter man at an auto parts store you can get either a 5/8" or 3/4"
( depending on the size of the hose )heater temp control valve that simply splices into the hose and operates by a cable. You don't have to hook up a cable if you don't want to but it might be a pain opening the hood to turn it open or closed without a cable. I got one for the original heater in my 37 Chevy and it is 5/8" inlet and outlet and I seem to recall it actually was for a 69 to 71 Ford pick up truck and cost about $11.00.
The actual original application doesn't really matter and you would be surprised to know that there are a bunch of different configurations in straight through and 90 degree in both single hose size and some valves have one spud of each hose size. A friendly parts counter guy who can still use a catalog is the key.
And finally it doesn't hurt a thing to have the valve closed if you don't want water circulating through the heater.
