Kevin,
There was no standard-equipment heater on a 1947 Advance-Design trucks (or on any GM truck during the Advance-Design years). However, GM sold at least two different optional (factory installed) or accessory (dealer or customer installed) heaters in 1947; and, other vendors also sold heaters that the dealer or customer installed.
1947 GM Fresh-Air Ventilator, Heater, and Defroster (optional: RPO 385) An Outside-Air (Fresh-Air) heater was available during all Advance-Design year (the style changed slightly in 1953).
1947 GM Heater and Defroster, De Luxe (accessory) This was only available for a few years.
By 1949, a less expensive Recirculating Heater/Defroster was available as a GM accessory.
Dash Recirculating Heater and Defroster Unit (accessory) If one of the above is your heater, let us know which one and someone will come up with installation diagrams/photos.
Tim
