Well, I tried booting the G4 off the G3 with the G3 in target disk mode. Nothing. I couldn't get a Panther disk (10.3.5, from 2004, says iBook G4 on it) into the G4's slot, and then when I finally did, (after also scratching the top surface of the disk), now I can't get it out. When I start up pressing C, it goes to the gray screen with the gray apple, and no sprocket, and doesn't want to go any further. I don't know if the problem is the drive, something else, or the scratch on the disk. But when I tried the G4 as a target again, the G3 did see the Panther disk as an external drive. Interesting.

I looked at the stuff about the logic board, and as far as I can tell, just from the things I have actually been able to get it to do, (open firmware, target disk mode), the display appears to be flawless. Right now it looks like it wants a new hard drive, new optical drive, and to figure out why it doesn't chime when I power it on.