I know the Trek 620 and 720 have chainstays of 18.5in or 47c. I think that's one of the main reasons why folks will pay top dollar for them.
What about other production bicycles throughout the years. It doesn't have to be touring specific. It can be an old vintage mountain bike like a schwinn high sierra or Fuji Thrill, or first year Specialized Stumpjumper.
Another side question: Anyone know where I can find the spec sheet for the geometry of early 1980s Kuwahara mountain bicycles?