I think that HDD size is not limited. Or limit is much much bigger than 480 GB.
Limited is only partition size - according to used filesystems.
I am using 500 GB HDD on Pegasos 2 ( MorphOS+AmigaOS4) and 1TB HDD on AmigaOne X1000.Here
is even article how to use 10 TB HDD on AmigaOS classic
I have no Powermac G4, so I cannot test it. But you can try:
- check again your partition size
- use 480GB HDD + adapter only single on cable
- try HDD in other MorphOS computer
- try other IDE-SATA adapter
- try SiI 3xxx PCI SATA card
AmigaOS3: Amiga 1200
AmigaOS4: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep, Sam440ep-flex, AmigaOneX1000
MorphOS: Efika 5200b, Pegasos I, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad