Update: the last time I tried to turn this thing on, it powered on but no display. Buttons worked, knobs worked, no lights. Something tells me somewhere I either bent a pin too far or broke it in the cable... I'm expecting I didn't break anything. I don't know too much about 80s/early-90s display tech, but I'm very certain that most things that would be connected to those cables, are not the kind of thing to fail silently when incorrectly connected. No pop and no smoke tells me I probably just missed a connection.
New cables on order. 100mm same-side 1.0mm 12-pin pitch FFC. Pennies. Then it'll be round 2. And, now I have the cabling to DigiRig this thing as well.