OSHPark.com has great prices and quality for hobbyist-sized runs of circuit boards, but you get three copies, so I want to take that into account in the design. In this case, I have three keyboards, so there's a natural division. That means six shift registers per board, 48 notes each, leaving a few spares. My pedalboard only has 13 keys, so I need a way to partially populate the board. Also, with 14 shift registers, we have a potential for wanting some buffering, so I want to make space for that on the board, but also create a way to leave it off if it turns out not to be needed. End result is here.

The ordering of the inputs to the shift registers looks odd, but it makes the routing much simpler, and is easy to arrange in the software. The boards look like this: