I have tried to modify OSInstall.mpkg in 10A222 to remove arch check, and it worked for that, however installation did not proceed failing with "did not find needed information". Have anyone succeeded with that?
The tutorial step you mentioned here applies to the versions of SL which do install and run on PowerPC architectures (i.e., Builds 10A96 and 10A190). As noted in the WikiPost, several core components of the OS for Build 10A222 dropped UB/PPC code entirely — Finder.app being the most prominent of these.
A hypothesis: the 10A222 mpkg installer, even modified, may be failing because it is looking for UB code in every package it plans to install, but in several of thee packages it is only finding Intel code, not UB code.