Looks like it will produce 20 kV.
The HV regulator is working, too. I can reduce the HV down to about 18.5 kV and up to 20 kV. When everything is working, I imagine I'll have to run it around 19 - 19.5 kV, just to have some headroom to maintain proper regulation.
I had also been thinking that if necessary I could try to add some turns back on the flyback. I won't be using the wire I removed, however, as you can see in the first attached photo. I didn't disassemble the flyback, but left everything enclosed in the core and frame while I unwound the coil. This meant that every few turns I had to cut the wire, to avoid having to pull a lot of wire through the opening. The insulation generally was destroyed as I unwound the coil anyway, so no use thinking about salvaging the old wire. Some new wire could be added with some kind of plastic mandrel walls to make winding reasonably straightforward. However, it looks like I may not need to do that.
The last picture shows a closeup of the flyback in the set. I coated the outside of the coil with some red insulating varnish. I may beef that up with something more at some point. I didn't want to glop too much on there yet in case I needed to add more windings.
As you can see, the focus rectifier is still not connected. Now I need to deal with the vertical dynamic convergence transformer issue and other things.