Well that was a fail. The unit powers up but the new screen stays dark. So either I f'd up those fragile-ass ribbon cables or it's a bad unit. Probably the former. Those ribbins are evil... I've reseated the two that come out of the assembled faceplate and connect to the main unit. One of those had been mangled a little and the white tab came unglued. I got it back in as far as I can tell with a little flashlight. Maybe it's the other one connecting the screen to the board...
Gonna run it dark for now, I don't have it in me to take it apart again... what a pain in the ass!
Anyone got a scrap one? Doubt I can buy new ribbon cables anywhere.
edit: I found the copper-colored ribbons on ebay:
https://www.ebay.com/itm/264953104853
But if the one that goes from the LCD to the board is broken, well, that one seems to be unobtanium.