The 601 was designed as a bridge between the old IBM POWER
architecture and the new PowerPC architecture. So it does a bunch of
things different/unique/wrong to make it more compatible with the
POWER chips so it would be easier for IBM to migrate. (What actually
happened though was that Apple managed to port MacOS from the m68k to
the PowerPC before IBM managed to port AIX from POWER to PowerPC...)

One of the big differences is that the BATs, which are one of the
virtual memory mapping things, work slightly differently, and can only
map much smaller subsections of memory. Dealing with the porting for
this would probably require deep understanding of the kernel.

Another difference is that the 601 keeps track of the time since
startup differently than the other PowerPCs ("real time clock"
registers vs "time base" registers). There are a handful of other
small things too.

If you aren't a Serious Kernel Hacker, your best bet is probably to
buy a G3 processor upgrade. :)

-- Dan