I noticed that early Campagnolo 1010 dropouts had a small hole drilled through just above the derailleur hanger. I would assume that this was for direct mounting of a non-Campy derailleur with an upper pivot spring. By catalog #17 (c.1973) this feature was eliminated from the 1010 dropouts.
Curious about this, I just removed the spring stop from the mounting bolt of an early Super LJ derailleur and bolted it directly onto an early '60s frame with this type of Campy dropout. Voila! a perfect fit.
However, this feature dates back to the earliest appearance of these dropouts (so, at least back to 1953) - many years before Simplex's first parallelogram derailleurs.
Does anyone know which derailleurs this originally may have been intended for?
Also, why would this have been eliminated? - Especially, when other brands of superior derailleurs were increasingly incorporating springs with their upper pivot bolts... (or, perhaps I have just answered my own question here).
Bob Hanson, Albuquerque, New Mexico, USA