I designed this case for the keyboard kit found here: https://keeb.io/products/levinson-lets-split-w-led-backlight?variant=6600662679582
It uses 7x m3 screws on each half to hold the top plate on as well as 4x m3 screws to hold the pcb to the inside of the case. There are 3 6.5mm diameter magnets on each half so that they can snap together to work as a single 40% keyboard.
I designed the right side to have a 2u space key which is more comfortable for me but you can simply use another Left Top Plate to give you 2x 1u keys on that side.
There are USB access holes on both halves for you to be able to flip the connector to either half depending on your desk layout.