Dear Dave,
The repair is neither odd, expensive, or hard at all to do.
The cable stop is a threaded one that was originally part of a Suntour front derailleur. It was easily removable from the Suntour derailleur - a nice simple and practical idea to allow many different cable routing options for the eclectic 1970's bikes.
Good bike shops try and hoard some of these sorts of little bits and bobs, because oftentimes someday they'll come in handy.
The repair is indicative of a clever and resourceful mechanic.
You didn't throw a Campy derailleur away easily back when it was rare and cost an arm and a leg. This derailleur has the nice early-style bronze arms - and a Suntour clamp bolt, to boot.
M. Fabian
San Francisco