Managed to find the bar-end shifter I needed to finalise this build, then spent a stupid amount of time messing around with various bits and pieces to get the cantis working.
There were various options for cable stops etc. stashed away, but finding something that would work took a bit of time -- and the result is something of a bodge.
For the back, I realised there was no hole through the seatstay bridge to bolt a cable stop to, and I didn't have anything to adapt dog-collar style, so tried a bit of a Heath-Rpbinson arrangement with a clamp meant to fix a rack to your forks. That was too flexy, but was consoled by the thought that the black cable stop would look better on the black forks up front.
Then I found a rear hanger designed to go on the seat collar, held by the bolt. But squeezing it into the existing Kona collar brought it too close to the seatpost, making it protrude at an odd angle. So -- more rummaging around and I found a 30mm seat collar which would tighten down just right on the seatpost. That makes for a very short hanger -- it would be much better to have one of those nice long Paul ones, but those are costly. Let's see how this version works in practice.
In front, the hanger fitted too snugly against the fork, so that it fouled the lower headset cup. It also needed a surprisingly long bolt -- and my combination of a crappy mild steel item with a couple of washers to make it fit not only looked horrible, but failed miserably to do the job. As soon as the lever was squeezed, the tension pulled the hanger upward and twisted it sideways -- to such an extent that the horrible bolt bent.
I briefly considered a hanger that fits below the stem, but it would need to hang down a bit more, like a
Paul Funky Monkey to get the cable in, so that was no go.
So I had to resort to a less attractive-looking but beefier version made by Tektro. It's the wrong colour which doesn't really matter, but it is shaped with a concave surface where it meets the steerer, making for a more secure fit. And I used a spare bolt from a Thomson seatpost which is more rigid.
So preliminary braking arrangements are sorted. All it needs is that bar-end shifter which I may be able to fit later today, and it'll be ready for a test ride.