Salsa Vaya with 11-42 & 50-34 downtube shift hydro brake by
Richard Mozzarella, on Flickr
This Salsa Vaya made a previous BF appearance as an orange frame with a bubbling cauldron of doom percolating from the seatpost.
It is currently adorned with the same Ene Ciclo shifters displayed in the eBay listing up thread. Though I got mine from QBP. The shifters shift an XTR rd-M-9000 Shadow plus derailleur & an Ultegra 6800 with 11-42 & 50-34 gears respectively.
The pull ratio of the rear derailleur is different than lesser speed groups & consequently it works just fine with the close together cogs. Shifting is a breeze.
The older Suntour friction downtube shifters with the small barrels are what I would recommend if using 10 speed so that you can more finely tune the derailleurs position. Be forewarned though, you will need nearly a full 180 degrees of rotation to use the whole cassette.
20190316_090930 by
Richard Mozzarella, on Flickr
20190305_163259 by
Richard Mozzarella, on Flickr
I wouldn't try bar end or friction thumbie shifters with SRAM derailleurs. IME the derailleur requires too much cable pull & the chances of success too small to be worth the effort.
OP: Have at it. There's massive street cred to "doing things the hard way" & even more when you're competent at it.