I think the biggest problem with this is not the difference in instruction sets, but operating system support for the hardware, which was embedded directly into system file. One of the tricks to the powerbook 170 hack was realizing that hardware support was partly in the linked patch resources. This is a kind of resource that was not used much before Mac OS 7, but was present in the Japanese version of system 6 that ran on the PB170. There is an outside chance that adding linked patch resources from OS 7 to the OS 6 system file might help. Of course, this doesn't do everything. All the other resources that support hardware, drivers, INITs, and a host of other system resources that support specific hardware may still stymie you. But in OS 7 there was an effort to focus hardware support into the linked patches.