This continues to be a fascinating project.

Your Dremel surgery was well worth it. That juncture looks much better now.

I think you made the right call with the slimmer, unthreaded brass tube.

That cutaway sleeve nut... did you make the cutout yourself, or can you actually buy them like that?

I also think you made the right call on not adding a spreader mechanism where the stave protrusions meet the brace. From one programming nerd to another, that would definitely be a YAGNI feature. (For non-nerds, that stands for You Aren't Gonna Need It. Programmers are bad about coding provisions for things that are extremely unlikely to occur, and this principle is a reminder for them to stay aware of that tendency.)