I've given up on the Mark XIII keyboard. The problem is that the small PC board plus the brass barrier was too big to position close enough even for MY hands. I've got a Mark XIV keyboard which uses different switches (surface mount SPST very short displacement). Soldered the switches directly to the copper wires I suggested earlier, and ran wires to the bottom, weaving them into a grid holding the keyboard firmly. Got them as I wanted them and put polycapralone on both sides as reinforcement. Have a folding knuckle rest, thumb rest, and palm heel rest. It's by far the smalltest keyboard I've made so far.
I'm using a wired keyboard this time, to see how compatible I can make it. It's based on the Teensy. It's very similar to an Arduino, but it can take on a USB Keyboard flavor.