I put in a whole factory A/C unit in my non-air 70 RT. I copied all of the holes off of the air firewall and cut the holes with a saber saw back in '86. No welding required! The only thing you notice, if you know to look, is that I don't have the lip around my blower motor, on the firewall. I decided to add air back then when I was sitting at a light one summer day, with my 440-4sp Challenger thinking that I was hot sh!t, when a plain jane 318 stock looking Cuda, coming the other way, turns left in front of me with his windows up. I suddenly realized that I was very HOT with a wet t-shirt on. I was lucky to be able to start collecting parts back then when Challengers and cudas were in almost every junk yard back then. I even bought a complete 3 speaker 70 dash assenmbly with ralley guages and all of the vents, switches,wiring out of a CONVERTIBLE 70!, for $500. I still have the dash in my car now and it never cracked! (those were the days!)
Rob