For a recent build I got shifter mounts that clamp to the bars (either common diameter, road or upright) and accept typical indexed or friction shifters (like downtube shifters). VeloOrange sells them; not particularly cheap ($65) but they work well, and don't look too bad. I put them just outside the center barrel of some road bars. Sorry, no photos, but you can see the items on VeloOrange site, and they even have a photo that's on an Albatross-type bar (bare, though) -- might work well with the bar-end reverse brake levers.
https://store.velo-orange.com/index....22-2-23-8.html