A/C Question...

It was similar to today's aftermarket A/C in that it was mounted below the dash. I was working for a Chrysler products dealer in 1964, and most A/C units in A-bodies were dealer installed.
You can install an aftermarket system that fits in the dash, but it's a lot of work and there isn't much room behind the dash because of the wiper motor and linkage. I installed a Vintage Air unit in my '64 and wrote an article about it...if you are interested.

http://www.slantsix.org/articles/vintage-air/Vintage_Air.htm