eMac can't boot recent kernels

Hello!
I updated my system a few weeks ago for the first time in a while, and
I am unable to boot the last two kernels at all. Those are
6.10.3-powerpc and 6.9.10-powerpc. I get an error from yaboot:

ERROR: claim of 0x1700000 in range 0xc2000000 0x10000000 failed
Claim error, can't allocate kernel memory

(Note, that I am still using yaboot because I can't find a good
explanation of how to boot OS X from grub. I have heard of a
workaround for it mentioned in other mails to the list but not found
it myself).

I managed to rescue my system using a netinstall disc to chroot and
add an extra entry to yaboot.conf for the old kernel that still works
(6.0.0-4-powerpc).

I note that the newer kernels are larger than the old ones, could that
be the cause?

Can anyone please advise on a route forward?

Thanks,
Ed