Hi the paragraph is worded oddly but of the 62xx and 63xx macs, only the 6360 can take a G3 Upgrade, it is a "L2' upgrade rather than a 'NuBus' Upgrade
Nubus is a 10 Mhz 32 bit bus used by the MacII series, Quadra series and x100 series PowerMacs, it was replaced in later high end macs by PCI bus.
the LC PDS bus was used in LC and Performa low end macs I tried to remain child-like, all I acheived was childish.