It is my understanding that OS X cannot be made to run on a 7200, no matter what; because the 7200's 601 is soldered to the motherboard, and 7200 CPU upgrades are really just 'computers on a PCI card' that don't actually kick in until their driver is active. Wow, was that ever a run-on sentence. (Sorry equill.)

Since XPostFacto can't use the PCI-card-based CPU upgrade, it can't boot OS X.

The lowest-end machine OS X can be forced to run on is the 7500 with a CPU upgrade to at least a 604. (I have run 10.1. on a G3-upgraded 7500, and on a non-upgraded 8500.)