Finished the AB register.  It's the same as the XY register minus 16 bit in and out to address bus.  I'm getting much better at the wiring.  For previous modules I would wire up just enough that I could test it, and then add  a bit at a time testing as I went.  This time I wired up the entire thing before testing, and only had one mistake when I fired it up (two bits crossed over on A).  It was a quick to spot and quick to fix.  My productivity should go up now.  I've also received all of my orders so I have everything I need to complete the entire system.  I dug up my label maker to tag the control lines.

I'm getting enough modules complete to start wiring them all together.  I can better judge now how many boards it will take for the whole system.   I wish I could buy the power rails separately.  I will be needing quite a few for data and address bus.