Context then question: I wanted to fix this, but couldn't get much movement without feeling like I was going to break something. Rib was detached from the lining, lining was still in the right place on the back (with a bunch of cleats from where someone repaired it before). The top of the bass wasn't particularly well attached, so I just went for it and popped the top (this pic is before I did anything, not sure why my photos get flipped sometimes). Got the corner blocks and linings mostly right, or at least a lot better, and put the top back on. Here's the same corner now. Let it all cure over the weekend, set it up and it plays beautifully. I did a relatively decent job I think, but the neck block glue joint wandered ~1mm north of where it was before (while first clamped) when I was gluing the tailblock. The result is that the neck angle is slightly steeper than before so I had to raise the bridge, and the ribs on the upper bout reveal about 1.5mm of unfinished top. It was not perfectly aligned (and not well attached) before from previous repair, I think I actually improved the alignment overall so I feel good about the repair and am going to play it as is, but I'm sure seams will open up again so at some point I'll likely try and do it again a little more perfectly. But that's my question - how do pro luthiers keep the ribs exactly aligned before the top is placed? Do you build a jig for each bass, or is there some secret I'm missing?