Re-labeling a bakelite'62 Valiant/Lancer dashboard knob

Bill Crowell said
I don't think it would be possible to reproduce the knob by 3-D printing because it has a quite irregularly-shaped slot in the back, designed to retain within the knob the spring clip that holds it on the lever.

Post photos.

There are things that can be 3D printed that can not be machined.

Also your not thinking outside the box. Perhaps a setscrew could be added or other device to retain it to the shaft.