I am curious, exactly how exact must an air conditioning system be? I could get an AC system out of a '74 Chevy Monte Carlo. Now, I know I would have to make up a new bracket for the compressor, and some mounts for other parts..... but is there any specific reason the system won't match .

Any serious reason, not just because "Chevy sucks and Ford ROCKS LOL!@!" etc, etc

 

i doubt it since they both bolt on in different places.and a compressor that old is r12 and you dont convert them that old it will last a month and lock up.honestly save up some money and get you a new r134a system youll be alot happier in the end. if your trying for a junkyard one 96/97 up cars and trucks are r134a but you could buy a used compressor that dont work.

 

Well, essentialy they are just another separate system, so if there is room for the box and condenser, I would think with modification for the mounting it would work.
The only thing that are unknowns are things like defroster hookups, and heater cores, and I doubt that those things would even be remotely the same.
If your looking for a system from a junkyard, I have found that .
many of Fords mountings through the 60's and 70's are pretty close, even some items in the 80's will interchannge
So dont give up On Ford stuff yet, there were millions of cars made in this time frame that may have just the AC for you.

 

They do the same thing - compress - the only problem you will run into is fittings for the lines. But, that shouldn't be a problem, as long as you buy the right ones. Ebay has a TON of compressors, for dirt cheap, and since you're making the bracket, you're all set

edit: Just realized you wrote the whole system. That may not work because of fitting everything under the dash, etc. But the compressor, that's what I was talking about. If you can find a stock A/C system for a mustang, get a new compressor from any vehicle

 

you guys are forgeting the 70s used r12 its super pricey today and the systems are lacking in cooling power.he needs a newer system 96/97 up for the r134a.r12 last time i priced it was 3 years ago was 70 bucks a 12oz can r134a is about 10 bucks a can the avg ac system uses 5 cans