If you got MacOS running again, See hfsboot part to get Open Firmware prompt. The first argument is to locate boot loader in HFS partition.
Number designates the partition number.
It depends your partition setup. OF boot command takes three arguments. Boot device name depends what OF recognizes, so that it varies machine to machine. 'devalias' command on OF may help you to find out the name to use. But this is not necessary strict. You have to know the name of file by other sources.