Hi Jonathan,
Maybe you misplaced screws to the upper shield and longer ones could make a short to the logic board. On the top shield only use the shorter screws. Also there's a known issue with the iBook G4 12" 1.33, the airport/bluethoot card socket can fail and cause kernel panics events. You may try to remove the airport card, reinstall the top shield and power the ibook. If everything works OK without KP then you'll know the culprit. Good luck...