It's been talked about before, some have mentioned the use of the under seat heaters from the 40's. The later suburbans actually have an A/C unit in the headliner that goes from front to back with individual controls. I have seen them in highly modified 1950's suburbans.
In 1967, GM installed rear mounted A/C units that provided cold air in the rear of the suburban. I believe these units can be installed in the earlier years, but I also think there would be a head room problem
