norcal49er,

I think I found a photo of a GM heater that might be like yours. It is in the 1947 Chevrolet Truck Data Book but it is not in the 1949/50 Truck Data Book (by then, your heater seems to have been replaced by a dash-type, "deluxe", recirculating heater). I'll scan a few photos and post them. It looks real interesting.

Tim

1947 ACCESSORY Heater and Defroster, De Luxe
1947 OPTIONAL Fresh-Air Ventilator, Heater, and Defroster