@Motorollin,
But those adapters only work with mice/keyboards that were designed to work in either USB or PS2 mode.
If you really wanna use the old A1200 shell instead of getting an A4000 keyboard, there's 2 ways of doing it.
1. Put the guts of an A4000 keyboard inside an A1200 case
2. Salvage a keyboard controller from an A500 and connect it to the A1200's keyboard ribbon and add a cable from the DBox's interface to the A500 interface. There's a hack on aminet that describes it in more details.