You got it Dave. The Henry J was a cost cutter and they didn't load it down with luxuries like a heater valve you could turn on/off from inside the car! You open it in the winter, then open the passenger side air vent so air can flow through the heater core and warm the inside of the car. The valve is supposed to be mounted at the rear of the cylinder head but in order to install the original type value, you had to remove a head bolt and a stud in order to thread it in. An owner of that car likely didn't want to do that and mounted it in the water pump outlet instead.
There is another way... and I've done it on mine. I'm not sure if I'd loose points for it, I don't think I did at Auburn, but NAPA has a valve that has a 45 degree spout on it which you can thread in without hitting the adjacent head bolt. Works fine and looks correct too, just won't match the one pictured in the parts book. I can't find the NAPA part number for it right now but I think it's still available.