Making significant progress.
I pushed up the SWCG yesterday and ran the filter all night on high. This morning the FC is 34 and the CC is 0, the water is totally blue, no green, but still very murky. I turned down the SWCG again and the robotic cleaner is vacuuming. I put some DE into the filter, and I'll be watching all day, and testing two more times. But I believe the algae is dead, murdered by being hammered with chlorine, and now just needs to be filtered out.

Again, since I'm not concerned with bleaching this old liner, I don't mind pushing the shock level to double the 15ppm recommended for a CYA level of 40. Obviously, I want the algae gone and my pool crystal clear again! However, I am totally confident I will get there today or tomorrow. Our BBB methods work. No magic involved. Kill the algae with lots of chlorine. Filter it out. That's it in a nutshell.