And it's done! Sort of, I guess. Still missing some minor finishing touches. But close enough that I might never bother to finish it all the way 
I present to you: The OptiplRX 570
The top panel got some scuffs and scratches (dremeling was fine, but that damn file!), but I don't mind - it fits the "old beater workstation" aesthetic. Need to get some mesh into the ODD slot, and I want to cut out the front I/O block and add a large mesh square there too. That's it.
Honestly, to me this kind of looks like it was built this way if I don't look too closely.
A peek inside:
Clearance? We don't need none of your fancy-pants clearance!
I probably ought to do some more modding here (the bottom fan (hard to see, behind the grille) is rather loud, and I think the offset mounting behind the grille is to blame. Turbulence and so forth. But that's for the future.
Lastly, the mesh:
I remembered I had some adhesive magnetic strips lying around (thanks for reminding me, [USER=10175]@SFF EOL[/USER] !), so I cut that to fit around the holes as best I could. Of course the adhesive is on the wrong side, so for now the magnets fall off if I remove the mesh. Not a big deal
I also did some stress testing: 45 minutes or so of playing Rocket League with the case closed, saw 235W power draw max and temps topped out at 73C GPU and 78C CPU. Did a Fire Strike stress test after that, which pushed the GPU temp to 75 IIRC, but still perfectly fine. As mentioned above, one of the fans gets pretty loud, but other than that, I'm very happy with this build.
