Tore down and rebuilt the valve body tonight. It was not nearly as nasty as I had expected, given the amount of lining in that filter. I'll put it together tomorrow and see if it changed anything. Got more work I'm doing, as well, so won't be driving until tomorrow afternoon.

Somebody has been messing with this transmission before. The drain plug in the pan had the Allen head stripped (grrrrr), and there was some line brackets and such left loose. Nothing in the fluid or the valve body looked nasty enough for such a catastrophic failure. Wondering if somebody put a used trans in it and didn't flush the cooler and/or torque converter after it lost a band. We'll see.