[blucar]

If the intent is to build a concourse correct vehicle then you are stuck trying to find a factory correct heater as described by Kube. However, for all practical purposes a car heater would do the job, most people would never know the difference.
My 36 Ford had a '39-40 heater in it when I bought the car in 1952. In the 71 years that I have owned the car, nobody has ever mentioned that the heater is not correct for the car.