Stickler,
Technically, if you want to match the original 1954 truck's "deluxe" heater, you are looking for an "Air Flow" heater from 1953-1955 GM trucks (it is slightly different from the earlier Fresh Air Advance-Design heater). So, the 53-55 it is slightly different from the heater that Achipmunk nicely restored.
The 53-55 heater has an interior door that is opened/closed by a cable-control. That cable-control was formerly used to open/close the defrost-deflector flap on the pre-1953 Fresh Air Heater. In 53-55 the Air Flow Heater's defroster flap was controlled with a lever/handle that is right on the heater body.
