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With the number of Airstreams on the road, there is a floorplan out there that will suit nearly everyone. There was some commonality to the designs for various eras. For instance, the rear full or 3/4 width bath was fairly constant from sometime in the late 1950s throught the late 1970s to mid 1980s. Beginning in the late 1970s, side and mid-baths became more common, and by the 1990s most coaches had some variance of the side or mid-bath.
My advice would to be to look at as many coaches as possible to get a feel for the floorplan and era that best suits your taste/needs/wants/desires. Then it will be an issue for shopping for the coach that is in the best condition in your price range and desired model. Sometimes, the exact coach will nearly fall into your hands without an excess of effort; while for others it can take months if not years of searching. With my Overlander, it was about nine months of searching; while it took a bit longer to acquire my Minuet as I was in no particular hurry to find a coach since I only wanted a smaller coach for weekends and shorter trips.
To get a better idea of what some of the Vintage coaches are like, you might want to spend some time looking through the website linked below:
In addition, if you haven't decided that your purchase must be an unpainted Airstream; there is the option of the Argosy -- the Argosy has some floorplans as well as features that either never appeared on Airstreams or appeared sometime later on Airstreams.
Good luck with your research and investigation!