Thanks to Mssrs. Moos and Broderick for their fine summaries. A couple of additional notes may be helpful:
1) Model 57. Unlike the 63/93/... which have the same 122 BCD, the 57 uses 8 mm. attachment bolts; the others use 10mm that interchange with most others in the industry.
2) The 63 left arms look identical to contemporary 49d, and the right arms use the same profile. In contrast, the 93 has a much larger squarish cross-section. I really like the 63s, finding them very graceful - but some folks think they look too light.
3) In my experience, it has been pretty easy to see if a 99 is early (23.5 mm extractor diameter) or late (Campy-style 22 mm): The later ones have slightly more slender arms, which have a slight offset relative to the sight lines of the chainrings themselves; the earlier series tend to line up the arm and the ring visually. But this may not always be true.
4) Over the years, I've had pretty good luck with SR cranks/rings that use the same 86 mm. BCD as the Stronglight 99. Some folks say the rings are softer, which they may be. The SR uses the industry standard 22 mm. extractor.
Things I won't ever do again in the US: tour with 14 mm. pedals instead of 9/16th (ever try to find a 14 mm pedal in rural Appalachia?). tour with 23.5 mm. extractor cranks. although I could carry a crank extractor...
Your mileage may vary.
harvey sachs
mcLean va usa