Well, after a long night of lather, rinse, reboot, I tracked down the "missing disks" problem to BootX 1.1.3. Presumably it's incompatible with MacOS 9? Anyway, with music playing I couldn't hear that the disk was spinning down just before booting the kernel and never spinning back up again. I got BootX 1.2b3 and it spun the disk back up during boot and that much worked fine.
It didn't fix the "architecture not supported" problem w/ the debian boot image though. So how much harder or easier is it to "bootstrap" the install with linuxppc and then convert to debian? J.