Okay, so the manual I have turns out to be for the powerplant heater. While it does provide some heated air to the cab, it's main function is to heat the critical components of the engine and transmission prior to start in cold weather conditions. This is one of the accessories/modifications developed for use during the Korean War (arctic/winterization kit) and involves some pretty intrusive installation modifications (re-arranging the location of items in the engine compartment, adding brackets, cutting holes, etc). Not what I think you are looking for. I didn't find anything in the Shop Manual...maybe someone else who knows more can chime in.
-Tom
