The next thing that I ended up doing was cutting out the posts to support the motherboard tray with. This should have been a really simple thing, right? You just cut four posts of the right length and you're golden. So that's what I did: I measured out 3.5" posts, and proceeded to cut them off with my dremel. (The extension was confirmed to indeed be miserably broken, so I ended up buying a new flexible extension... and what do you know, it works perfectly!) Unfortunately, the cutting wheel wasn't quite large enough to cut through the entire dowel smoothly, so the ends were, uhm, slightly uneven. Here's a before and after picture of a dowel that I've sanded down to flat and a post that I've just cut, on an even surface: After a lot of finicky sanding and evening... it works! It works beautifully, and I'm thinking that I'm all set. Unfortunately, then I try putting the motherboard, power supply, and hard drive on there, just to get an idea for the tolerances that I'm going to be working with. Guess what? Those posts, that I just spent a good amount of time making perfectly even? Are too thick. The power supply can't fit between them! So I have to go back and cut out new posts out of the much smaller square dowel. I still have to figure out a way to make these work perfectly, but I think I can do it.