Experts Question re: Dealer Added Factory Options

[Nufsed]

Hey folks, I usually hang out over in 60-66 but I'm up against some confusing info on a '71 I'm looking into.
first: the truck is on the East Coast and I'm in TX.
The current is the second owner and he bought from the estate, so no contact or conversation with the (deceased) original owner.
I've received a *bunch* of pictures. I've looked at all the details to the extent that I am able.

This '71 is a low-mile "survivor" with a repaint but not a restoration.... and no Krylon, anywhere.
The truck a *nice* 71 C10 2wd 350 TH swb
The truck has Factory AC.
The weird bit: The truck has all its docs, SPID, even the window sticker.
Everything is awesome except that the AC is not listed.
I'm not new at this; I've checked all the indicators for correctness that I can see. The VIN tag has the right rivets. The S.P.I.D. list matches everything on the truck saved for the air.
The AC is clearly all of the correct factory pieces, and would appear factory installed.
Now, back in the day, the dealers could buy "up-option kits" to install items that were not ordered on a particular car, for example cruise control. The Up-option kit had ALL the required pieces to install the cruise exactly like the cruise in the factory installed units, right down to the rubber grommets. Once installed at the dealer, you could never tell that the cruise was not factory.
I'm aware that dealer installs of "hangdown" AC was prevalent at the time (I recall $400 for it) but my question is this: Does anyone know if the factory ever offered an Up-Option Kit to install the **factory** Air? It would've been crazy expensive and very involved to install, but I'm left wondering if it was ever offered...and maybe done to this truck??
I'm certain the firewall is different, so it would be really odd.
Anyone have any ideas to explain this install, assuming the cab and VIN and docs are legit?
(trying to post pics...standby)