If you do not have the original AC/heater box in good condition then I wouldn't even ponder trying to reinstall a factory system.  Every one of those boxes I've seen in the past 20 years has been cracked, shattered, cobbled back together with epoxy, etc.  Its just not worth messing with.  Any modern system is going to be better than 50 year old junk.

A modern compressor is also going to be much better than the old ones that drained like 20-25HP off the engine when engaged and had the weight of a boat anchor all the time.  

Lucky you if you have the original control cluster and the left, Center and right hand side vent outlets. They are reproduced in some kits but nowhere near the O/E quality.
There  are at least a couple of aftermarket ac units , mine is a Classic Auto Air, Vintage  Air is another.
I’d suggest calling one of those companies and explain what you have and I’m more than sure that one of them will suggest what parts you need to complete the installation.
You probably don’t need a complete kit since an original A/C car will have a lot of the ancillary components.
I found CAA has an excellent customer service.

The original system was 12 volts, so I'm wondering if you (daily driver) are confusing 12 volts with the coolant R-12 freon?
The 12v runs the blower motor and the compressor clutch solenoid. All Mustangs, all the way back to 64.5 have had 12v electrical systems.

GPatrick wrote:

Maybe the OP is looking for a fully electric A/C system?  Here's an example - https://mightycarmods.com/blogs/news/cool-runnings-electric-air-conditioning-allows-a-c-in-any-project-car?srsltid=AfmBOorXl53zgo3yEN06-05IjG3hoSmg9ThN-ofdNFxcANjRcuTSqFNm

 
That's what I took daily driver's original post to mean. The compressor is powered electrically instead of a belt drive, which allows you to mount it in the trunk if you'd like.

GPatrick wrote:

Maybe the OP is looking for a fully electric A/C system?  Here's an example - https://mightycarmods.com/blogs/news/cool-runnings-electric-air-conditioning-allows-a-c-in-any-project-car?srsltid=AfmBOorXl53zgo3yEN06-05IjG3hoSmg9ThN-ofdNFxcANjRcuTSqFNm

Wonder if a compressor can be sourced at a Tesla boneyard?

 
DD needs to clarify Zackly what system he is asking about.
I checked Tesla a/c compressor and it runs at system  voltage 350-400 and draws 5-20 amps not 12 volts.
There are numerous articles on the net about 12 volt driven compressor conversions.

Thank you everyone for your responses.
Happy New Year Everyone.
Sorry I didn't offer more information.
GPatrick is correct, I was referring to a completely electric system.
But that sounds like just as much work. I don't know. I hope not to run anything to the trunk.
I thought everything would be in the engine bay.
I'm ok with the compressor on the engine because it came that way and I still have the crankshaft duel  pulley. Sounds like a lot of work either way.
@TKO  I have the original air box installed. I replace the heater core in 2013. I believe the air box is ok.
But I trust it probably isn't and would soon fail anyway. 
I have a 289 engine with an Edelbrock torquer 289 intake. I disconnected the AC vacuum control lines way back in the 80s. The Max,  AC, fresh air, defrost knob isn't function right now. I would like to have defrost again too. I've been plugging the diaphragm vacuum line going to the heater core for heat. 
All help is appreciated!
Thank you

Here are a few videos of an install 

=13pxhttps://www.youtube.com/watch?v=ttDs310PJMQ
https://www.youtube.com/watch?v=alXXXS5neCs

Considering the need for a larger battery and a 150 preferably 200 amp alternator, a serpentine setup with a belt driven compressor seems to be the better alternative.  You likely won't be able to drive an alternator of that size with a single v-belt.  It looks like an electric compressor is a good choice when there is no other viable option for a belt-drive.