Have you ever used 640s with a PowerBook 1400? The SCSI on that machine doesn't seem quite up to regulation. I can get things to mount on a G3 Wallstreet, but the1400 won't cooperate at all.
Did you ever make any progress on this issue? I picked up a couple of 640 drives from Japan for cheap. Most Adaptec SCSI PCI cards were Mac Compatible. I have several.
I use the generic IDE/SATA ones on eBay with 2.5" SSDs or you can install 2 port or 4 port SATA PCI cards. The 2 port ones support OS9. You can flash cheaper PCI cards yourself if cost is a big issue.
https://www.ebay.com/itm/314911045287
https://www.ebay.com/itm/264812274223...