I picked up a couple of Dark Tower PCBs. I contacted an ebay seller who offers a repair service and asked him if he had any broken PCBs, and he sold me one. Right after that, a tower came up for buy-it-now at a (somewhat) reasonable price, so I got that, too.
The bare PCB has some battery acid damage, but the chip looks OK. I decapped it and I'll Whink it tomorrow to make transcribing the bits easier.
The bare PCB is Rev C, while the PCB in the tower is Rev B. The Rev B board has a DIP TMS-1400; the Rev C board has an SDIP. They are wired the same except that Rev C runs an additional output to the chip enable of a hex driver that controls the speaker and lamps. I'm not sure why; maybe to make it easier to blink all the lamps at once, or maybe to shut them off to save power? The Rev B board also has another transistor hacked onto it for motor control. I guess the original design wasn't robust enough.
The motor rotates an inner plastic shell with 21 different different images that the lamps can illuminate. An LED and phototransistor are positioned to detect notches in the shell for indexing. I haven't figured out how to remove the inner shell to get pictures of the images, and I'm not sure how to get good scans since it is curved.
The tower was listed as not working, but after I put it back together it seems to be fine.