The 8881 was a red herring. As Ian pointed out in the comments, the output is an open collector, so it won’t be high until BUS DC LO pulls it high. In fact that gate is only pulsed on power-off, not power-on. So that chip is probably just fine.
That said, I’m still completely lost. There is definitely something wrong with the power-on sequence, but I can’t for the life of me figure out what it is. I’m going to step back and take a break for a few days and see if inspiration strikes me.
What I really wish I had was a known-good KD11-A to compare against, but that is very unlikely to happen, alas.