Probably the easiest option is a modern "knee knocker" which have become pretty slim line. Add a drier, a Sanden compressor, a modern crossflow condenserand the appropriate hoses/lines. I'm doing it the harder route: change the firewall from a non-AC firewall to a factory AC firewall and use all the factory underdash hardware and all the underhood pieces with the exception of the compressor, where I'll use a Sanden.