HRMMM, if you can get it to allow bootup when set to another ID in another Mac or in the same Mac with another HDD set to 0, or from a DiskWarrior CD in the 650, that may solve your re-initialization problem.

Does your 650 have a CD?

Have you tried booting from a CD?

Try removing the termination SIP resistors if that's what the HDD uses, or pull off the termination jumper if not, and try a CD/terminator on the chain.

I used to use a Centronics 50 A/B switchbox for semi-hot-swapping problematic SCSI devices with termination on the A side and a bare terminator on the B side for troubleshooting. With the proper cable setup, you could use a DB-25 switchbox for the same process.