A quick update on current progress: the second board for Register File is now complete. It is a 16-bit 8-to-1 multiplexer, almost the same as the previous board, only this one has additional 3-state output.
Next will be a "backplane" board for registers. That board will have some logic on it (a couple ICs), and many connectors to which individual small register boards are to be connected.
Here is the photo of Src1 selector board: