The cape board PCBs have arrived from China:

I placed a few components to ensure that the physical fit was correct. Since I created the Eagle PCB parts for the SNES controller sockets, I wanted to ensure that all of my calculations for the layout were right:

I put in an order at DigiKey and Raphnet Technologies for the necessary parts, and I'll begin assembly of the first few prototypes once I get the parts in. In the meantime, I'll keep working on the software for the BBB's PRU that bitbangs the gamepad interface signals.