Richard,
I am surprised that you do not think much of the huret duopar (either the eco steel model or the titanium model.) Frank Berto, who is a hero of mine, considers this to be the best-shifting derailleur of the early 1980's (better than Suntour VGT, although not as light as Suntour Cyclone, which are two of his other favorites.)
The super-weird SLJ derailleur on the header page of french components is probably the strangest thing i've ever seen from simplex :
http://www.classicrendezvous.com/
I have never seen it in a catalogue. I have several used SX-410's (low-mid end, some with S starbursts like SLJ but not SLJ) with long cages, please write to me if you are interested in one ($18).
- Don Gillies
San Diego, CA