you can make a Powerbook Aluminium boot into OS9, but you loose almost every feature of the machine: the left side ports are all dead, as is the Airport. Firewire may or may not work at 400 speed, the right side USB port for obvious reason is restricted to USB-1.
Network looses auto-negotation (you have to set speed on your router, which seems 100/half duplex though System Info says 10/half duplex).
No energy related functions and screen dim available, graphic acceleration abstent, too.
The only advantage is that it remains silent and OS9 Audio software works.
In my case (Alu 1Ghz 15") it was the ROM file that prevented booting in the first place and then the Multi-Processing system extension, which gets easily overlooked inside it's folder.