Your confused... Snow Leopard is the last Mac OS that can run PPC apps for OS X through Rosetta. It will run PPC apps but it will not boot on a PPC machine. The kernel doesn't support it and even if you did rebuild the kernel and enable PPC support, there would be a whole bunch of dependencies that just wouldn't work.
The PPC binaries that are required to boot and run OS X on PPC are just not there in Snow Leopard, the GUI support for PPC is also not there and would need to be recompiled and then some of the remaining portions of the OS are simply hard coded for Intel CPUs only specifically apps and system resources where the source code is completely unavailable where the code itself would have to be completely rewritten.
It cannot realistically be done even if you overcome the first hurdle of recompiling the kernel so it boots to the command line. It will panic as soon it goes to load the desktop.
What you'd try to achieve is what ReactOS is trying and failing miserably at, and that is completely rewriting an operating system practically from the ground up.