Fascinating... Perhaps one of the levers went to the valves in the engine bay to regulate the flow a bit so it wasn't just "On" or "Off", the 2nd lever switched between defrost and cabin with the third switch for fan speed?
Personally, I would retain it as it is unique and from the era. If it were a cheap obvious hack i would go back to factory configuration, but these look like nicely chosen and executed period correct mods.
MH