Nice car, the seller is obviously very proud of. Those aftermarket A/C units were popular ad-ons back in the day. Not as desirable as an original equipment system would be but not totally out of place either. You could call it period correct.
I might add "location correct", too. From what I remember down here in DFW, the add-ons were popular in the earlier '60s when the factory units were costly, in comparison. By the middle '60s, the market had swung more toward factory units than add-ons. A good add-on could also include an upgraded generator/alternator and radiator (which came with the factory units already).
Mopar AirTemp had two different versions of their "hang-down" accessory a/c units, as did GM and Ford. All of the Ford factory units were "under-dash" until the 1965 model year full-size cars, when they became fully-modern integrated units.
By 1970 "Texas", if we saw a newer car with hang-down a/c, it meant the car probably was sold in an area that didn't get that hot in the summer. OR somebody screwed up in ordering the car.
When Chevy came out with their "Special Economy Truck" 1/2 tons in the middle '80s, they had an equipment configuration geared toward higher mpg. Didn't include factory a/c, either, so a local vendor put together a bolt-in unit that was hidden behind the instrument panel. It worked, but had a noisy blower motor. 5.0L V-8 5-speed manual smaller tires, lowered ride height.
CBODY67
