So no one has bit into this one? I have a 51 but the horn ring is round if you will. I have pictures somewhere of how they look when they are apart if that would help you. Mine has a round flate disk that is concave or convex depending how you look at it. Then there is a brass plunger that slides into a sleeve and mounts under that disc. When you press the horn ring in flattens that disk which makes contact with that brass plunger affair and the horns should sound. Is yours like that or are you missing those parts?
The chev club sells a replacement kit if you need them, and I could email installation pictures.