Optical drives have been of standard size since about forever. (OK, since at least the early 90's they've all been of standardized size.) Of course, the notebook-size drives have also come out, and they too, have a standardized size!
Anyway, a G4/450 is definitely an unsupported configuration for a SuperDrive, but there's no real reason it shouldn't work. (But it has happened that older G4s get funky with SuperDrives, so be prepared that there might be a chance that you'll have to swap the drives back.)
tooki