I don't know the SCSI spec all that well, but it's a well documented general computer interface standard from the MiniComputer era. Theoretically, you should be able to convert USB or ANY other interface to 68k Macs over SCSI.
On the Mac's totally un-compliant SCSI implementation of the SCSI standard things get a bit tricky. I don't know about the Compact Macs, but in many later Macs there's a shrouded MoBo header for a terminator block just inboard of the the external SCSI connector.
This is reversed in the DuoDock, which uses this same setup on the internal side of the SCSI Chain, which allow for an optional internal HDD setup.
SCSI Adaptation for earlier Macs more than likely makes troubleshooting a ClusterChain of significant proportions!
Suggestion:
Active Termination entails adding electronic components for auto-sensing termination of the SCSI Chain, which is entirely different from just having termination active.
I'd suggest sourcing an external peripheral case with the Active Termination Circuitry built into the Dual Centronics 50 Connector/ID Switch PCB to add to the end of your chain.
That's always been my first test for troubleshooting SCSI Voodoo!
