Two firms that I know of made chain-stay mounted horizontal
parallelogram derailleurs.
Altenberger made some, which Charlie Kuhn still has NOS at Kopp's
Cycles, Princeton
http://koppscycle.net/
Suntour also made line of these, late in the day.
And, Chuck Harris made his own Back In The Day.
Anyhow, I think this stuff is High Funk, and I'd like to find an Altenberger or Suntour rear that is workable but not pretty, and pretty cheap.
thanks
harvey sachs
mcLean VA