Zooming in on the breadboard itself, you can clearly see the power and ground wires for each chip (power is at the bottom, ground at the top). The main difference between my schematic and this design is that the control lines and carry in will eventually be located at the far right, instead of in the middle. A and B lines are still on the far left, though, and you can see I've started to run lines from them to some of the chips. I still don't actually have switches for the input lines yet, but I'll figure out how exactly I'm going to do that later.