I replaced my Key Assigner with an Arduino. As a result, it was written in C/C++, using some of the Arduino libraries simplified wrappers for reading and setting the digital pins.
Note that I was also doing a bunch of other changes (replacing the keybed with a MIDI-outputting keybed), so my Key Assigner software would not be directly useable with the Polysix's built-in keybed, but adding the key scanning wouldn't be too big a deal.
Here's a post describing the start of the hardware replacement (swapping the Arduino for the 8049):
http://synthhacker.blogspot.com/2013/03/polysix-replacing-8049-key-assigner.html
Here's a post describing the timing of basic activities in the 8049:
http://synthhacker.blogspot.com/2013/02/polysix-basic-key-assigner-timing.html
And here's a post describing the sharing of my code on GitHub: