A crude method that could be used for interfacing future projects, as well as the current one. While only needing to interface with eleven, 4-bit circuits, it's logical to have spare and sixteen works out nicely. Use of binary 0000 - 1111 with a 74154 which "Decodes 4 Binary-Coded Inputs into One of 16 Mutually Exclusive Outputs" and jumper holes for desired circuits address, we are able to relay "electronically switch" between PCB's.

For complete circuit diagram, view this binary-interface02.png link.
The BinaryInterfaceSelector.sh script, makes changing PCB's easy with a pick of 0 - 15, then displays pin values.
Wiring diagrams of input interface-bus-cable.png and output interface-bus-cable2.png cabling.