Note here in the photo that you can see that the fan is taller than the enclosure (it extends above the metal “rim”). When I was reassembling I inserted and removed the fan three times assuming that I had mis-aligned it somehow!

I needed a tweezers here. These screws are tiny!

If you lose one you may have to remove the RAM (by pulling the appropriate lever) and gently slide out the screw.

You need to replace the shorter middle screw first, otherwise it won't tighten later since it won't quite reach the bottom.

You need to replace the shorter middle screw first, otherwise it won't tighten later.