How to make a livecd for powerpc

Hello,

I'm trying to learn how to create a livecd that will run on PowerPC (specifically, a G4 Mac Mini) and boot into a minimal shell environment with a few basic tools available.

So far I've been taking inspiration from the Jessie installer DVD (debian-8.11.0-powerpc-DVD-1.iso) with the goal of just getting _something_ to boot.  Taking a look at /.disk/mkisofs on that image and removing everything related to Jigdo I've ended up with the following:

genisoimage \
    -joliet-long -r \
    -V 'Debian 8.11.0 ppc 1' \
    -o 'test_live.iso' \
    --iso-level 4 \
    --netatalk -hfs -probe \
    -map ./hfs.map \
    -hfs-parms MAX_XTCSIZE=15625000  \
    --chrp-boot \
    -part -no-desktop \
    -hfs-bless CD1/install \
    -hfs-volid Debian/PowerPC_jessie \
    CD1

However, trying to boot an ISO built with these options (including kernel, initrd, yaboot, etc. also taken straight from the installer disk) in qemu with

qemu-system-ppc -L pc-bios -boot d -M mac99,via=pmu -m 2048 -cdrom "$image" -nographic

just results in

/pci@f2000000/mac-io@c/ata-3@21000/cdrom@0:0,yaboot.conf: Unknown or corrupt filesystem
Can't open config file

Burning the image to an actual disk and inspecting it it with `diskutil info` in macos shows that
it has a filesystem of "ISO Rockridge" and partition type of "CD_ROM_Mode_1"; for comparision the official Debian installation disk has a filesystem of "HFS" and partition type of "Apple_HFS".

The NetBSD boot cd instructions (https://netbsd.org/docs/bootcd.html#macppcimage) suggest that further steps are required after the initial creation of the ISO to modifiy the partition table and render it bootable by appending a driver file of some kind.  However, having had a rummage through the debian-cd 3.1.17 build scripts for Jessie, I can't seem to find any post-processing steps for PowerPC that look promising.

Can anyone with more PPC experience please point me in the right direction?  Given that all the pieces I'm using come from a known-working Debian installation DVD, I suspect I'm just missing some small option or step, but all the livecd tutorials I can find assume x86.

Thanks,

--
Mike