The radio / clock / display says my battery is at 12.1v. Everything else electronic seems to be okay. There's no dashboard indication of a security lockdown. Some research suggests that a bad crankshaft position sensor might be causing the issue.
If you know these cars, then you know I had to disassemble a lot of stuff, unplug a lot of wires and disconnect a lot of hoses. I am fairly confident I got them all back in, but wonder if there's anything specific I should try next. I'm pretty sure that one of the wires I disconnected before was the CPS, and I'll try re-seating it again while I wait for an answer, and will update if anything changes.
I'm also having vacuum issues with the "crankcase ventilation primary" actually disconnected or broken. I haven't been able to trace it back to where it belongs so that I might replace it. I only mention it in-case it has relevance to this current issue.
I tried the trick suggested here:04 Cadillac cts no start key stuck sidestep fix, and it cranked, but did not spark. While trying this though, the display showed "Service Theft System".