> I'm a big SCSI guy, but ...
 
I too am an old SCSI fan, but my interest started to wane when so many SCSI signalling standards and connectors began to proliferate together with SCSI moving totally into the high-end server realm and away from "ordinary" peripherals.  Oh, and then there was that "termination power" headache (usually selected/deselected by jumpers).
 
> The device has a standard dense 50-pin 2-row connector.  I thought at first that meant for sure LVD, but now I'm thinking it just means ultra.
 
It doesn't even mean "ultra", let alone HVD/LVD.  That connector became the norm during the single-ended classic SCSI 2 generation - to my great chagrin, since the Centronics 50-pin connector was so much better.
 
> Is there a way to know what signalling this device uses based just on the connector?
 
No, but:
 
> I checked all available interent specs, incl the original manual, for the device and *nothing* specifies anything other than "SCSI".
 
Since the original manual (lucky you to have that!) doesn't specify anything other than "SCSI", it is a near certainty that this isn't LVD or HVD, but simply good old single-ended classic SCSI (of at least SCSI 2 generation).  It probably isn't "ultra" either, especially if it's a scanner or CD drive or similar slow device rather than a hard drive.