This is a great guide, thanks! I have a 636CD (currently running), so I'm going to save the link for future reference.

Re: preparing the blank IDE drive for the performa: wouldn't it be easier to use a SATA/IDE to USB connector, if your OS 9 Mac has USB? (Maybe that's rarer than I think - I use G3s and G4s to run OS 9.) That would save opening the OS 9 machine. Just plug the IDE connector and power cable into the drive and the USB into the USB port. Or have you tried that and it didn't work?