A quick trip to Radio Shack, and I got the components to hook up the Symbolics keyboard with Teensy. I didn’t even alter the keyboard itself as Hans Heubner did: rather I just used a standard 6-pin RJ25 socket and connected the Teensy to that, then plugged the keyboard in, and put the connection assembly inside a little project box. Then it was as easy as recompiling the Teensy firmware for my Teensy version (2.0).