There's no real need for a processor for remapping a KBD Matrix. A simple ROM/EPROM Hack will give you whatever output you need from any given input, when programmed with the appropriate I/O matrix.

IOW, map any given KBD's keyswitch matrix ribbon cable output, using connectors stolen off MoBo or KBD Controller Board soldered to a home-brew (Radio Shack still carries all needed to do simple, SS or DS, PCB etching) adapter board as your Input. Solder the donor controller board directly to the adapter board for best results or jumpered with patch wires if spacial constraints necessitate this approach for Output/Native Controller conversion.

IIRC, Don Lancaster spec'd this setup in either the TTL Cookbook or the CMOS Cookbook. [] ]'>