The final stage of the assembly was less time-taking than expected. Fortunately the new button mount proved extremely effective, and I'll be using the exact same method with future builds.

So, first job today was to solder up the switches and LEDs:

Once this was done, the buttons were attached to the special platform I'd made earlier:

The buttons basically run 1 through 4 from bottom to top, with the fifth button being "shift". It would be nice to have them labelled, but I haven't figured out a way to do that yet.

The button assembly without doubt demands the most precision of any part of the build, and for this reason I'm surprised it went together so smoothly. The first thing to establish was that the buttons were all sitting in their recesses at an even height:

I'd previously slid the platform into place and marked the centre points of the switches with a pen through the holes in the top of the case. Once everything was lined up, I was able to glue the platform in place:

Because the base has to be 100% sturdy, I epoxied one end of the platform to the front of the case, and the other end is supported by part of a wooden coffee stirrer which just happened to be the correct height!

Once I was sure everything still worked, I glued the LCD display in place with epoxy resin:

I also superglued the remote LEDs into their holes in the case (the power LED is connected to the +5v line of the SIO connection with a resistor: not sure why but I've never been able to get the power light to work off the usual spot on the PCB with these things), and cut the SD card slot into the bottom of the case (shown here before finishing):

The penultimate job was to epoxy the PCB to the bottom of the case (I had done several test runs previously, and just a couple of internal protrusions on the case had to be trimmed back to get everything to fit). Once the glue was set, everything was ready to close up. Note in this picture I haven't yet attached the SIO cable to the header (it's secured with a cable tie where it exits the case to prevent it being yanked out):

And at last, the moment of truth: I closed up the case, plugged in, and powered on:

A VERY satisfying job, not least because the design has become so much cleaner. There are still improvements I could make (such as labelled buttons), but it seems the XM301 was almost made to house an SIO2SD board. Once I'm sure everything works after some tests, I'll screw the case together with the remaining screw pillar. It does look like the other end will have to be glued shut, however, since one screw isn't strong enough to hold the whole casing together.