It's a Hitachi Ultrastar IC35L073UCDY1.  I have tried either and both "Force SE" and "Disable Parity" and neither - no effect.  I have not tried Unit Attention yet, nor have I tried the what I assume is wide negotiation (? TI SYNC NEGO ?).  The documentation I found said it's compatible with G3/G4, but I'm not too familiar with SCSI on those machines.

This was intended for a standard 50-pin Power Mac 7100.  I tried both of the two adapters I have for 80- to 50-pin.  Also important to note I have an Apple CD 300plus in there - or whatever the stock drive is called.  The CD drive is jumpered with ID 3, Parity, and Termination Power

The Ultrastar drive has a bunch of jumper options but I'll omit the IDs etc.

FORCE SE

DISABLE UNIT ATTN

TI SYNC NEGO

DISABLE PARITY

DELAY START 6 / 12

AUTO START DELAY

DISABLE AUTO SPIN

I need to sort of do a DOA test on this one versus whether it's just not compatible.