I can't answer all the questions but to my knowledge there is no control to stop the flow of water on the 'non-deluxe' (round core) heater. I have one in my 49 and it basically blows air from inside the cab. On the deluxe heater it draws in air from outside through the louvered vent on the right cowl.
My 1949 price list does not show the either heater as an option so I might think the regular heater came standard and the deluxe may have been a dealer install. I am sure someone will have a more definitive answer.
If your heater has a square/rectangular core it is probably easier to replace than a round one.
