Interesting... I think that I understand what you've done, but just to be sure...
The stop surface that the workpiece aligns against is the bolt head, right?
And you do gross length adjustment by sliding the tube through the rectangular bracket and hold it there with the black handscrew?
And you swing the stop into place or out of the way, then tighten the bolt that connects it to the stand?
I haven't looked through the rest of your blog yet, but will I find pictures of your flashlights there?