Have the FWB Harddisk Toolkit software (HDT). I managed to use it to set up a PB 180 with several partitions on the internal harddisk drive. Each partition (=volume) may contain one blessed system folder. Use HDT to configure which volume shall be the standard boot volume for a given SCSI ID (which is stored in the PRAM as a boot volume). You may force the Mac to boot into any bootable partition at early startup by use of a key combo (it is like cmd-opt-shift in combination with the partition number). To get the details read the manual, please). The version of HDT I used was 2.0.1.

FWB Inc. seems not to exist any more, sadly. Is there any supply of the most recent HDT version available ? The version number stalled arround 5, I think.