Installboot on Beige G3

Hi There

I am trying to get NetBSD 10.1 installed on an Old World Beige Mac G3
with Openfirmware 2.0f1. I realise this is marked as difficult on the
model page but this is what I have so this is what I am doing!

After Install from CD (using a Zulu SCSI) I am dropping to a shell and running:

# installboot -m macppc /dev/rwd0c /usr/mdec/bootxx /usr/mdec/ofwboot

This is asking me to provide "-B bno" which I am having difficulty
understanding what is required for this value.

I am installing to a CF Card installed as ide0.

I have a working OS9 Cd I can boot with System Disk available so if I
need to make any changes there I can.

Any Advice on how to proceed from here would be greatly appreciated.
It's quite  frustrating as I have Gentoo booting via the Bootx app but
really I would like a NetBSD only setup on this box.

Thanks!