I put together a preliminary layout for the input PCBs and ordered them today. I'm using SN74HC32 4-channel OR-gates and SN74HC165 parallel-in serial-out shift registers to read sets of 8 notes from the keyboard. Here's the layout, as rendered by OSHPark:
Sometimes, the easy way turns out to be a little bit harder than you thought.
As I will explain as soon as I get to the keyboard layout explanation post, there are some pairs of keys on the keyboard which play the same note. I had initially planned to connect the common pins of each pair of keys and have one connection on the circuit board, but I realized that I had missed something painfully obvious about that approach.