That was the first version of 1952. The 1951 versions are even rarer, and probably more expensive. The final, mass-produced version was introduced in 1953.
There was an article on all these early Campagnolo Gran Sport derailleurs in Vintage Bicycle Quarterly Vol. 2, No. 2.
140 Lakeside Ave #C
Seattle WA 98122
>Anybody been watching this one?
>Wow. Not the seller, and no chance of being the buyer....
>Ottawa, Ontario, Canada