Finally got a chance to try out the experimental version of 
installboot that preserves Apple Partition Maps.

I can report that it seems to do no harm.  I copied all the 
distribution files to sd0a, and then got the new versions of 
installboot and bootxx on the root of that partition inside the 
install kernel.  I then used the new installboot with the -v option 
and copied the output by hand:

./installboot -v ./user/mdec/ofwboot ./bootxx /dev/rsd0c
boot: ./usr/mdec/ofwboot
proto: ./bootxx
device: /dev/rsd0c
proto bootblock size: 1024
entry point: 0x006c0000
./usr/mdec/ofwboot: block numbers: 1987952 <other numbers> 1988048
Blocks are 1024 bytes for 2 blocks
Found partition map with 63 entries.
Found free space in partition 9
Updating freespace partition 9.
Partition now starts at block 4193407 for size 8.
Expanding active partition count to 10.
Installing new boot blocks.
Size 2 blocks, starting at 4193405

After doing this I can't boot to scsi-int/sd@0:0 or any other 
partition number.  Don't recall the exact message but it's something 
about forcing partition 0.  If I leave the ':0' off then it gives 
something even more terse like claim failed.  If someone would 
suggest a specific boot command to try I'll make sure to copy the 
exact error message.

The machine (a 8500) can still boot MacOS when I type bye.  After I 
got it back into OF and fixed the variables as usual I could do a 
'boot scsi-int/sd@3:1,OFWBOOT.XCF netbsd.gz' to start the install 
kernel from cdrom.  The above had just failed when this worked so I 
know nothing had changed to acount for it.

I also saved a dd of the first 10 blocks of the disk if that's of any 
use to anyone.

Signature held pending an ISO 9000 compliant
signature design and approval process.
h.b.hotz@jpl.nasa.gov, or hbhotz@oxy.edu