There is "another" ROM that allow the "Spring 2003" iMac G4/800 "Flat Panel" X Only, to boot into Mac Os 9.
 I've taken a little time comparing that special ROM (convenient called "Custer") and Mac Os ROM 10.2.1 and I always thought that are almost the same thing. My therory is that the Custer ROM upgrades Mac Os ROM 9.8.1 to 10.2.1, but I may be wrong.
As I haven't any FW800 to test it.  I can share This ROM to any one that want to experiment. ...and who knows...