Well, I got the bevel cut down to size, put it all back together, and - DEAD.
I can't be sure, because there's no way to see in the photos, but I might have disconnected the power wires by accident. I have a blue and red wire that seem like they come from the battery, and which are now ending nowhere.
Oh well, killed it.
It's not like the Caanoo was worth playing MAME games with the vital parts of the top and bottom of the screen obscured, anyhow.
Maybe the Dingoo will be better.