Big day today…
Short version is that when I drilled the caliper mounting holes in the first bracket , somehow I goosed it entirely.
I don’t know how I got it wrong, because everything seemed perfect but I drilled them as though they were for an 8mm smaller rotor - I seriously considered making the rotor 8mm smaller, but the mounting lugs on the caliper and the upright were touching.
So, begin again (admittedly with a big headstart from the earlier experience).
I needed to machine up four spacers to laterally align the caliper correctly, and again was hamstrung but a lack of lathe tools.
Did manage to track down a beautiful turning bit, but also needed a parting tool.
Instead of using a parting tool, I used a hacksaw, which is a slow, dangerous and miserable way of doing things, and then each spacer needs to be faced again (which is not fun to set up when they are 8mm long).
Anyhow, it all works.
Final task was to provide clearance to the webs on the caliper mounts but that was just a couple of minutes with the linisher.