Well, I had to figure this one out by myself - it took longer than I expected, but all is working now. I guess a bootable RAID array is not as interesting as the newest video card... !
I flash my BIOS on a regular basis, and from the release notes, "New Promise BIOS(ver:2.0.00.23), can support 130GB or higher HDD". It looks like they also changed the menu options and how the "*" works to indicate a bootable array. The other thing is not to follow the manual - don't make SCSI the first bootable device, make it third, with floppy first and CDROM second. Also, install OS without the 3rd drive in place. Once the system install is complete, put the HD back, boot, and let the OS find the new HD and do the setup. I suspect that with the 3rd dirve in place, the OS was writing the MBR to that drive, but I'm not sure about that. This worked for me, I imagine other ways will work too.