Maybe some of you have seen this if you lurk Deskthority, but a member there (tlt?) has a great project where after successfully using a Teensy to use his C64 as a keyboard, he decided to rebuild the keyboard in the C64 with Cherry MX switches. Anyway, he created these C64 switch (I forgot what they're called) to MX switch keycap adapters from Shapeways, and of course, I ordered a set.
It is by no means perfect, but it is by all accounts, awesome.