Sounds like an SX 410 T/P (or GT/P if long cage). The angled upper pivot models were SX 610. The SLJ derailleurs were all alloy, but they don't function any better than the SX models--they're just lighter.
The SX models were originally sourced on the mid-range models from the French builders.
> Calling all francophiles: What model is this Simplex rear derailleur in
> my parts pile? I'm lost in a forest of Simplex models, and am guessing
> it's a "Super LJ Model 5500" from the mid-70's but correct me if I'm
> wrong. From a review of the archives, here seem to be the relevant bits:
> vertical parallelogram geometry; aluminum upper and lower pivot castings
> both with "S and star" logo; black steel mounting claw/ear; chrome steel
> pivot bolts; bronze w/ black lettering badge "Simplex"; parallelogram legs
> are steel w/ a black Delrin(?) infilling; short cage; Simplex plastic
> jockey/tension wheels. There seem to be tiny, illegible partial stamped
> numbers/letters on the rear of the upper pivot casting, and a larger
> partial "D" or "G" (?) stamped on the front of the lower pivot casting.
> Maybe all this detail is a "so what?" but there seem to be so many Simplex
> derailleurs I'm lost. What bike should this go on? Any details I left
> out? I can email pix, sorry I don't have a site to post them on. I know
> some of the Simplex derailleurs get trash talked, but have to say I got
> thousands of trouble-free miles from the Delrin "Prestige" model on my
> first Peugeot.
> Reid Fisher
> San Martin , California