Mnemonic did a rump-esque controller replacement for the M and 122 M a while back, it's not too bad. I tried it out at the time.
It's a bit more work to assemble the parts and solder them up, but if you breadboard first, to test, it'll be straightforward.
The project is pre-disk-hell on the server, so the thread is in the archives and doesn't have working pics anymore, though.
Enjoy - I wish everyone took the time to put together their own controller.
So many things about the keyboard become more clear in there: exactly how the matrix works, debounce, USB descriptors, etc...
dfj
