oneclick 

Flatten out the shifter band and drill out the back of the boss where it is riveted into the band.
Stop when you just get the point of the drill into the circular base of the boss, then it should punch out and leave you a nice flat(-ish) surface.
Dress the surface with a file and make the edges of the impressed lines distinct - they are very useful as guides later on.
Cut a slot in the back of the boss so it slips over the braze-on boss.
- I used a hacksaw and files and a good vice.
- I cut a slot in the end of an M5 screw and threaded it and a washer into the boss from the lever end, so the the washer would catch the underneath of the vice jaws and I could tighten it with a screwdriver from above; this to keep it tight down against the jaws.
- You have to be careful to make the slot parallel and square and just the right width and depth; check with the end of the other boss, that's what you want to match.
- When you have the slot just right drill out the threads of the boss with a 5mm drill, and find yourself a longer M5 screw, then put t together.
- Left as exercises for the reader:
a) make a filler bit for the gap next the frame;
b) make a (pair of?) travel stop(s).

Bianchi84

That's a beautiful-looking bike; what is it? As far as filling in that gap, I remember there being flat aluminum washers meant as brake caliper spacers. I was going to suggest the curved version, but it seems like you can adapt what you have to what you need.
They look like this... but I can't find a direct source right now.

bark_eater 

I wonder if the different Suntour Power Shifter thumbies might provide some of the bits needed. I stole these pics from Velobase.

dddd

Is there anything now preventing the lever from swinging down into the wheel and preventing free steering movement?

Does a lever stop not also help prevent one's hand from moving too close to the gap atop the tire under the fork crow?

I hope that I am missing something and that the installation does offer some lever-stop function(?).

Did Suntour not offer a braze-on version of these levers? (Guessing not).

I'm suddenly feeling luckier to have come across a good few retrofriction levers for sale in the wild (where the clamp-on ones are the more scarce!).

oneclick 

No, there are no travel stops (as yet - but see last part of original post...)

oneclick 

Sannow - this one:

https://www.bikeforums.net/classic-v...-japanese.html

MrGastrognome

While I appreciate the ingenuity here and love the feel of Suntour Power, I'm not as fond of their appearance. Why not use the DiaCompe reproductions? All the clicks, none of the Q factor issues... or does that take all the fun out of this project? I picked up a pair to replace my power shifters (as they look more like the original shifters on my Team Fuji) but haven't found a clamp I can mount them to yet.

Kontact 

Especially since later shifters had finer ratchets.