I've been watching the thread and am very impressed with Winston's work on using a wheel center for a horn cap!
I'd mentioned in an earlier post that I had a possibility other than seeing if the Chevy cap may have similar clips. What I was referring to is that I have family members who own a metal fabricating shop. They have computer controlled Laser and Waterjet cutting equipment and manufacture all sorts of production and one-off items. I sent a photo of my horn cap showing both the broken and intact clips to my uncle and he believes that they could make a new clip using spring steel banding material of the same gauge. Now the dilemma I'm having. He asked me to send in a clip, preferably the broken one IF I had the broken off piece as well as what remained. Otherwise, he would need an unbroken one to scan and model. I checked the floor of the car and the recess behind the horn bar and I cannot find the broken off bit. Because of the issue with the clips being attached to castings rather than being simply riveted on, I'm hesitant to remove an intact clip as then I'd have only one good clip left and the center cap would be useless if I messed up trying to drill and tap the castings to reattach the replacements. I don't have a drill press and would be very nervous about trying to use a hand drill make the holes.
On a positive note, it does look like very small taps are available https://www.victornet.com/detail/TAMP-1.6-.35.html as well as screws. Just need to determine the length that would be needed.