My favorite Cherry keyboard used to be with DIN connector. After upgrade of my PC, I still wanted to keep using my old trusty keyboard. A small PCB taken out of PS/2 to USB interface fit in the room around LED status indicators PCB. The USB hub required more work, to be available at the keyboard back edge. Two of 4 USB connectors were saw off. One of them is unavailable anymore, while the other is used to connect PS/2 interface PCB.
PC XT/AT keyboard
with enough room to fit components inside
PS/2 to USB converter interface
just the bare PCB