Last night I followed Drew's suggestions: removed all PCI cards except for the ATI graphics, and connected the partitioned hard disk to the internal bus. Clicked on XPostfacto, and asked the computer to start installing Panther.

It rebooted nicely, and installed the OS until completion. Great!

I restarted the G3 hoping that it would load the newly installed operative system, and crossed my fingers.

To no avail. The screen comes up with a "happy Mac Plus", and hangs for at least 30 minutes.

Sigh, I pulled the plug and went to bed...

More things to try: change to another motherboard, with freshly zapped PRAM and newly pressed CUDA, an original Beige G3 IDE 4GB, and OS 9 on an external SCSI.

Unless there are other and better suggestions?