The G3 must have the "Silk" ROM, and the Bit 3 must have the 3.3v Power Supply as well as the IBM 85353 chips on the Main, Host, and Controller boards. To verify these:G3 models M6503LL/A, M7104LL/A, M7246LL/A, and M71006LL/A have the Silk ROM. If you have a model other than this, open the G3 according to Apple's Hardware Installation Guide and find the ROM slot labeled "ROM DIMM"located in between the "SGRAM ONLY"slot and the 3 "DRAM DIMM"slots. If there is a ROM in that slot, check the label on the U1 chip. The Silk ROM is labeled "KMM264V515A03-10P, 9829"The Power Supply for the Bit3 7-slot chassis will read either "+5V," or "+5V and +3.3V" on its label. (Note: The +5V Power Supply has 2 connectors that go to the Main Board, whereas the +5V/+3.3V Power Supply has 4. The connectors from the +3.3V Power Supply are labeled P8, P9, P10, and P11, but the connectors on the Main Board are labeled P8, P9, P11, and P12. P10 from the Power Supply should be connected to P12 on the Main Board, and all other connectors should match.)All three Bit 3 boards have a PCI Bridge Chip, and these must be IBM chips with "85353" in the part number. IBM chips with "85352" (as well as DEC chips) are not supported with MIX systems.