Ok, first ride, after fitting brake blocks and putting a washer inside the drive-side dropout. Light. Bars look wonderfully retro, but don't suit me at all. Will look for flatter, narrower ones a la Scott/Trek.
Braking is not great, although definitely needs more fettling. Will convert it, maybe, to nutted long-drop dual-pivots.
Gears: DT friction shifting not fun from high flat bars. Much wobbling! Probably better from lower bars, and with more experience. But indexing looms large in my mind. Less concerned about the FD, only two rings means one way or t'other, so may try and find a thumb shifter with a friction setting.
So, far from perfect, but a promising start.