An A500 case/keyboard combination could easily used as a keyboard for any big box Amiga. A1200 & A600 have the keyboard controllers on the mainboard and would have to be heavily modified.
But why? If you're missing the A3k keyboard, you can use any A2000, A3000 or A4000 (with adapter). An A1000 could be used with a DIY cable (lacking reset capabilities) and a PC keyboard would need an appropriate adapter (e.g. Lyra).
