Here's the deal...
The new knob is bigger by about 3/32" in diameter. You can see it overlap the raised center of the black housing a bit, whereas the original knob is slightly smaller than that raised part of the housing. I thought I was being so clever to buy a Z50 switch and rob the knob off of it. I was then going to put my old knob on the Z50 switch and sell it to recoup a little of my money. To my surprise, and not in a good way, the Z50 knob is slightly larger in diameter. It still fits, and to the untrained eye, seems to look normal. Unfortunately this becomes a $50 knob, and incorrect at that. It is fully functional and works properly. Unfortunately, the smaller broken knob won't fit on the Z50 housing, as it won't seat fully enough to allow the circlip to be installed.
Did any other models, even completely different Honda models in 1974, use the smaller K3 knob or was it unique to the K3 CT70? I wish CHP would reproduce these knobs. I've seen plenty of posts saying the same thing. If it had worked, I had planned on making a casting mold or creating a 3D model for possible 3D printing, but it was not to be.
What do you guys think I should do? Use it until the correct one comes along (pretty $$$)? Do you think a concourse judge would notice? (not that I'm anywhere making this that good)
I also wondered what the correct color red was on the originals or if they darkened over time. The new one is pretty bright red, although it has a pink tinge in the pictures, that's just the lighting.