Snap off all external boards. Don't split the sidebars if you're using 5x6.
If you're using a 4x6 configuration, break off the bottom row.
Use a knife/file to scrape off the jagged edges of the PCB joints.
The 4 triangle pieces can be soldered onto the 3 pads near the USB ports to reinforce that area.
To configure USB ports: There is a column of 3-pad jumpers above the MCU. Solder the middle pad to the pad in the direction of the port you want to connect to the PC. Do this for all 4.
On the slave side, solder them in the opposite direction.
Test your keyboard!
Use the supplied pin headers to line up and solder the spacers onto the top of the LED board.
Cut the long leg off the pin header.
Put the pin header through the holes, per the image below.
Flip the boards over, and make sure the holes are lined up.
Solder the pins in, and trim the remaining pins
Pull the plastic headers off and trim them as flush as possible. Add solder if needed.
In the end, your LED board should look like the last image below.
Solder switches on with plate/case.
Trim the pegs and pins as low as possible (<2mm height).
You may want to do this in the PCB or out, whichever is easier for you.
Be careful not to break any of the surface components on the PCB.
On the master side, solder the 2 pads marked "Master" together.
On the slave side, you'll need to put some tweezers/jumpers into the two holes marked below next to "Master".
Place nuts into cutouts in the case or plate. The screws are screwed up from the bottom, sitting inside the cutout you created in the first step. You may need to push the switchplate back down and/or force the nuts in.