These images are from Campagnolo Catalogue #17 copyright 1974. Which covers Super Record, Record (Nuovo Record) both Strada and Pista (Road and Track), Gran Sport as well as Valentino. These attached pics are the exploded view of the Brake levers. I also looked in Catalogue #14, Zippo. The piece you are asking for does not exist as a Campagnolo part. There are ferrels on the ends that insert into the lever itself but do not have a split in them.
I did a little research. The item you seek, I believe it's from a Universal Brake part that has a split in it that sits on top of a brake lever. It has a conical shape, made of aluminum, a side split that sits in between the cable casing and the brake lever. Correct me if my description is wrong. This piece I’m describing based on my past experiences can be found on Schwinn mid level models (Super sport, Internationals etc) as well as others.
Sorry for the delay reply.
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People in the cheap seats Boo the loudest