Resolved! In case comes across this in a search with similar symptoms, here's what I did:
1. Since I meant to recap the analog board anyway, I went ahead and did that
2. After recapping the board, there were no real changes to screen flicker, but I was able to boot all the way to Finder and...
Until recently, this machine has been booting from either the internal HD or images from a BlueSCSI just fine (albeit with some of the applications that I was testing crashing the system with the same "error type 11"). I've been getting this message once the machine tries to run Finder...