I printed the parts on a Prusa Mini, with PLA filament, on a smooth PEI sheet. The gcode was generated with PrusaSlicer 2.6.0. The 3MF files with the exact print settings and part configurations are available on the Releases page.
The body halves are printed sideways, with custom supports. In PrusaSlicer, custom supports can be added in the Object list (Advanced mode). Right-click on the body object and load the support STL with "Add Part". Right-click on the support object to adjust its print settings.
Note that there is not much room between the switch plate and the PCB. Therefore, I soldered the diode legs on the same side as the diode body, and cut the legs reasonably short on the switch-facing side with a flush cutter. To hold up the PCB while soldering the diodes, I used standoff jigs that clip into the stem holes (see photos).
The diode pads have a common pitch of 7.62mm (300mil). To bend the legs in a uniform way, I used a bender jig. Both jigs are available on the Releases page.
The PCB halves are connected via Flexstrip jumpers. To compensate for the default split angle, the strips should be folded in a specific way before installation. Check the image for reference. I wrapped the strips around a thin screwdriver shaft, to maintain a minimum bend radius of about 2mm.
To install the PCB, I would first clip the corner switches into the body, e.g. switches 12-64-58, 10-9-6, and 49-48-45. Then align the PCB with the switch pins and push it flat against the switch bottoms.
Before soldering any switches, check that the screw mount next to the Pico does not bend the PCB. If the print is misaligned, you might want to sand off a bit of the mount, or extend its height with a washer.
When everything fits, the remaining switches can be inserted. Note that the thumb switches are north-facing (upside down).