Can anybody tell me the difference between the "Automatic Temperature Air Conditioning" option and the "Custom Air Conditioning" option available on 1970 full size pontiac'* (bonnies, cats, etc)? My car was delivered originally with the "Custom" version, but it needs to be replaced. I found and bought a NOS "Automatic" version, but now that I am looking at the two side-by-side, it is clear that they are different. I consulted my shop manual, and it'* not entirely clear ...
1. what the original functionality differences were intended to be
2. whether these units are interchangeable
3. what additional parts are required to facilitate the interchange (if any, and if possible)

Anyone know anything about these units?

I tried some searches on the net and only came up with this small tid-bit of info for the 1965 model year. Hopefully, someone will know more than this, though.

http://www.pontiacserver.com/mtengr3.html

The term "Custom A/C" was basically manual A/C. It did NOT have an automatic temperature control. My father had a 1968 and then a 1971 Catalina with Custom A/C. It had a **** you would turn and the indicator would show how hot (red bars) or cold (blue bars) you wanted the temperature to be. The **** controlled the blender door that controlled the heat.
These units are NOT interchangeable
I have no idea what it would take to make "Custom" into an "Automatic" unit besides a lot of money and the parts and labor it would take to convert the unit.