Non-ac car needs air conditioning

Yes, the AC firewall is much different, at least in my 1965 Dart. A few people cut out most of the firewall to weld in an AC firewall, but seems extreme. There are new generic heat/AC climate boxes which fit behind-dash, as cheap as $400 (ebay, Amazon). They use a battery remote, not your dash controls. A few companies (Vintage, Classic) make retrofit climate boxes which fit better. Otherwise, consider an under-dash "knee-knocker" AC box, either vintage or new (~$100). But, then you have 2 separate fans and ducts which adds clutter. I'm a cheap-bastard so went that way, plus didn't know the options when I bought stuff.