I am using 3000/240 to write this mail.
To get OF without ADB keyboard, you may need MacOS and BootVars.

(1) Have floppy with BootVars copied. (MacOS:HFS)
    ftp://ftp.netbsd.org/pub/NetBSD/arch/macppc/macos-utils/bootvars/
(2) Run MacOS. MacOS CDROM boot may be fine.
(3) run BootVars from the floppy. Set variable as
  auto-boot? false
  input kbd
  output screen.
  write and reboot.

This case also applies if you don't have serial port connection.
---
Makoto Fujiwara
http://www.ki.nu/software/NetBSD/iBook2/