It's been a few years since I installed OSX on my iMac 233 MHz Rev B Bondi, but I did not need to use XPost Facto. I upgraded the internal hard drive to 13 GB (non-Apple) and partitioned the drive so the 1st partition was just under 8 GB. I installed OS 9.x, upgraded the Firmware and installed OSX 10.3.x

I didn't have any card installed in the Mezzanine slot - that may present a challenge to installing OSX.