I am going to install an aftermarket A/C in my '73 500 with 351C, 2V and would like some tips and comments regarding Classic Air, Vintage Air, or others, what problems I might anticipate, and what parts/kits may cost. There is no factory A/C in the car so I will be starting from scratch.
First question we'd need an answer to: are you wanting to install the factory-style parts (evaporator case, ducting, etc.) or just the Mark IV-style underdash unit? As far as compressor choices go, they're all similar to the Sanden compressors; you just need a bracket and pulley kit to drive it.
I looked pretty hard at both before deciding on the Classic Air - my biggest reason was that the Vintage heater box is glued shut, and if you ever need to replace the heater core (which I've heard is frequent ) you need to cut the box apart. The Classic setup went together fairly well, instructions were good, and the fit was about as good as could be expected.
I didn't do the under dash deal, mine was in place of the original heater box. Cost? maybe $1100 or so.