That cable isn't considered detachable. And, it has a different connector from a non-detachable Lexmark Model M's cable, so that idea won't work.
Besides, with a pin adapter, an AT keyboard will work just fine on a PS/2 system (or PS/2 to USB adapter.) This seems to be an XT keyboard, which will need a protocol adapter (ClickyKeyboards sells one of their own design for $100

) to work on an AT or PS/2 system.