I have looked into the same thing myself. I picked up "How to AIR CONDITION Your Car", Remus & Chisenhall, Published by MBI at the local Barnes & Noble. They install AC in old cars, trucks, street rods and kit cars using mostly Vintage Air parts and info. Very informative, but as chevy1 said, you are still doing a lot of fabrication.
The local pick-a-parts have mostly late '80s cars. Most GM AC have always required the fire wall to fit the AC. Half of it in front of the firewall and still have large units under the dash. Mopar are mostly under the dash but usually have messy hoses and the AC lines often enter/exit on the drivers side. I hate to use the F word, but many of their units are very compact. Some are not too much bigger than the Vintage Air units and all the hoses come out in one general area. The factory AC always have fresh air intake that makes them a little larger than the aftermarket units. It would be easy to eliminate this feature. I intend to look for one of these units when I get around to that project on my '67.
