The scene is finished! That was some arduous shit, man.
Yesterday I had all this resistance to working on it and just pissed away all my writing time on the internet, and was really annoyed with myself by bedtime. So today I woke up and vowed that I was not sleeping again until the scene was done. Not perfect; just done. It probably took a total of three hours over the course of the day, which is actually pretty horrifying for a 2,500 word scene that I'd already fussed over for days. But whatever-- the bastard's done. And so much better than it was.
I changed my mind again and decided to hold off on the "history lesson" dialogue. I think that was the right decision: it was turning into a "As you know, Bob..."conversation, and there's scene coming up soon where I think it'll fit much more naturally.