The new axle plate makes mounting the wheel a lot easier. Will wait until I sort out the disk before making the dropouts 10mm. When I narrow the dropouts, I'll add a bit more metal for the torque plate to press against.
Not sure if the 160mm rotor will work. The amount of rotor that is available at the disk mount looks a bit short.
Could get a few millimeters more by making the dropout deeper, but not to much more, else the axle nuts will hit the tube.
I'm not the first to have hassles with the rear disk mount. I'm hoping that it will not take me too long to sort out.