I had to try this at least once. The lever is 5/16" all thread covered with a piece of chromed toilet supply line. Knob is an old magazine cap from a Remington 1100.
Retro Rocket's 3x7 grip shifters moved into rocket body. Switches for headlight and tail light at top of each shifter and the wires travel through the shift tube and collar, then through the extension springs into the rocket body.
Working on stick shift 2.0 for my Townie now. Got the shifter itself working well, but need to develop a better mount. Not opposed to making a tank plate and bolting the shifter to that, but I'd like to find a "smaller" solution.
All thread rod with toilet supply cover as earlier model. Knob is a wooden "Doll head" from craft store and cover plate is a cover for a bathtub over flow.
*** UPDATE ***
Finally worked out the kinks. The new mounting clamp is a chainlink fence part. The original clamp has been moved forward to keep the nose of the shifter from going too far up when downshifting into 1st.
I upgraded the custom shifter on my Electra. No more clamp on lever, this one is "geared" right to the grip shift.
Took a little time to carve out the teeth on the aluminum lever and the PVC spacer, but being quarantined lately, I had some time on my hands.