I wish I would have read some of the comments, especially about needing a particular kind of adapter to install a 2.5" SSD. A note at the top about this would be the only way to improve these most excellent instructions. I found a stainless steel, vented adapter that has one open side, and a connector for the SSD. The outside of the case has the SATA connectors in exactly the same place as a 3.5" HDD, so the lack of slack in the SATA cables is no issue. The metal is thick enough to properly seat the mounting pins. I don't want to violate any iFixit TOS, so I'll just say that the unit I bought, a 3.5 Inch SATA Bay Adapter Converter Bracket Mounting Kit, is very, very cool. Freezing cool, a perfect dock for your new SSD.

Prying the plastic bar that locks the HDD into place was probably the most difficult part of the operation, for me. It just didn't want to let go, and until you've actually removed one, it's not exactly clear how it's holding on. The left side basically has a thin wedge on the back that wedges in between the rubber grommet and the mounting bracket