Now you're talking my language thorsen!
My area of expertise starts with the 1970 introduced /5 series and ends with the 1995 end of the Airhead line. I gravitated toward them early on and for some reason began buying and selling them, along the way keeping a few.
If you're asking for yourself, e-mail me and I'll launch into a diatribe that would cause most forum members to mutter under their breath.
But basically any of them can be used for about any purpose if you take into account speed, load and distance required. You can take a 1970 500cc bike across country and you can go to the corner store on a 1995 R100. They are light, simple, long-lived and while not as comfy as a full-on modern touring bike they are reasonably suited for a long trip. Many of the models have integral fairings but many are built "naked" and the owners can choose from a multitude of aftermarket vendors for bodywork and luggage.
Right now I have a 1967 R60/2 that is in the process of a more modern (1976 R60/6) engine conversion, a 1976 R90 that I have owned since 1987 and have set up as a naked roadster with some aftermarket upgrades and a 1985 R80RT (owned since 1990) that is original except for an R100 top-end transplant. I also have a 2000 K1200LT that is up for sale, hopefully to finance a different style of tourer.
Don't know what you want to know but I'm glad to share. Let me know if there are specific questions or if you are shopping for a bike for a specific mission.

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".