[AzDon]

I had a friend once that claimed to have been born with a full set of teeth..... He'd say that at an early age, he learned to keep his mouth shut!.... Translation: While he MAY have been more advanced, he was only answering questions he was asked rather than impressing others with his knowlege!
It's okay to ask questions and opinions, it's how we learn! It's impossible to know how something was originally when it all is missing!
I recently bought a 92 caprice wagon with the heads off and all the parts thrown in the back of the car. Unless I had also bought a 91 Custom Cruiser wagon, I would still be scratching my head about parts placement!
My opinion on the factory air and heat.... almost all that I've seen place most of the guts under the hood which looks ugly and detracts from the beauty of the engine and your ability to work easily under the hood. These burbs have plenty of inboard space for an evaporator/heat unit!
My preference is for one of these evap/heat units with defrost. Nostalgic Air has a variety of units that would be great on a burb. As far as a rear air unit is concerned, a rear air unit from 73-87 can be fitted to look like chevy put it there and will give you good additional cooling in a lightweight and compact package!