I am not sure of any of this anymore, and I AM a product of the '60s, so this could all be a hallucination...

BUT, I think some of the older aftermarket air systems I have run across have used the factory, non air controls and placed a decal/ sticker on the face, showing a/c. Almost positive I have seen some older GM stuff this way, at least.

This used the off position (IIRC) as the a/c position. Maybe vent?

Not sure of this, and all of the stuff I have is factory air ... maybe someone who has a non air truck could look at their controls.

Might be worth a call to Vintage air or one of the aftermarket companies, maybe some old timer like me but with a better memory could help you ...