Your shifter was part of a system which included an aluminum chain carrier that bolted onto the inside of the rear Campagnolo dropout ala the two small holes. The chain carrier acts an auxiliary cog sized and shaped to accept the chain as it is shifted off the smallest freewheel cog. The idea was this allowed faster wheel changes. By keeping the chain indexed to the dropout, the rear wheel could be removed and a new wheel installed with no messing with the chain. After the wheel change, the rider needed to be pushed in order to shift the chain back onto the freewheel. The small rounded lever kept the main shift lever from over shifting onto the chain carrier until a wheel change was needed. The rear triangle needed to be respaced to accommodate the chain carrier.
I have a NOS chain carrier and tiny bolts, but no shifter.
Kevin Ko
Eugene, OR