Just to be safe, you might try booting from the LG drive with a retail OS install disk.
B&W G3s are kind of picky about which optical drives the will start up from.
I used to have a B&W with a Lite-On burner, and a firmware update made the drive non-bootable.
This page has many user reviews of drive upgrades in Macs.
Note: To boot a PCI graphics G4 from an OS install disk, hold the C key. G4 and earlier Macs with PCI graphics don't have the Option-boot feature.