[AZKen]

Even if they could tell from mounting holes, what value did it add to the ad and what value does it add to the truck? If he has original dealer paper work showing purchase/installation of Air, that's kind of good. If not, any under dash unit could have been there during any era of it's life. Done by PO.

As said, probably a good old honest guy with little knowledge of vintage trucks. Translation: stole it from a widow neighbor!
As you can tell, this is a dealer.