Does the enclosure have a pushbutton SCSI address switch?

Admittedly grasping at straws here, but you might try this:

Disconnect the enclosure switch(make note of which wire goes on what pin) from the drive and set it to an unused address ID. VS is commonly set to 7, so don't use that.

With a VOM, determine which leads on the switch have continuity for the SCSI ID chosen above. Write this down.

Use jumpers to replicate the continuities determined in the previous step.

Connect and try. Keep trying jumper configs until it either works or you run out of IDs.

Just a thought.

~dk

Just on a surface observation -
1- that appears to definitely be a scsi hard drive. It's very thick compared to a "standard" pc hard drive, correct? So, my usual orientation to things like jumper pins is totally useless.

2- From the looks of the 3rd photo - hard drive from above - that white thing in between the ribbon and the power looks like a jumper block to me. What is it used for?

3- What's that mess of heat shrinked and otherwise individually connected wires coming from the "front side" of the hard drive being used for? That is evidently what the diagram on the hard drive label is referencing then, correct?

So your ID is connected via those pins at the front?

I still see jury-rigged wiring on that connector - the large bulb of heat shrinked wires pushing/bending against one of the pins next to it, for instance. That's not factory is it? What's that connector all about, I wonder?

I can clearly see that the burner has an easily identifiable pin diagram that shows where a jumper would go, so that's nice - simple for simple minds like mine!

Aside from these observations, I am still at a loss to understand why the hard drive won't function since the os update.
Did you perform the update with the external unit connected and turned on? Maybe it would make a difference to do the update again, but without any external devices turned on, except for the zip drive used to update the os...... Or is that the way you did the update?

I wouldn't think it should have mattered whether or not other scsi devices were connected and/or turned on/off while doing the update, but it might be worth the time to do the update over again???? I don't know if that feels like a waste of time, but one can never be sure without trying.

What else is there to assume, but that maybe the hard drive has stopped working - even in that 1/2hr you spent updating the os - weird to be sure, but is it possible?

Only way to find out would be to try the drive connected to some other gear - a pc maybe - or to try a different drive in this enclosure.

You might need to scrounge up another hard drive to know for sure what's up with the one you have in that enclosure. You might try getting a scsi1 to scsi2 adapter to try out that other drive you have... if you can find or make one.

I wouldn't know how to make one - it's just a notion...

sorry to confuse your midi update with another's zip update!
I prefer the midi method, myself.

That drive is marked “LVD”, which means “low voltage differential”. I very much doubt that drive has ever worked with any VS machine, or ever has.

https://www.seagate.com/nl/nl/support/kb/lvd-ultra2-scsi-low-voltage-differential-drives-196471en/

Apparently, LVD and SE devices are (should be!) mutually compatible. I did not know that. They’re bound to be even more finicky than SCSI always is, though.

How do I configure termination and termination power on Seagate LVD drives?

Do to the specifications of Ultra2 SCSI, Seagate LVD drives have no provision for setting termination on the drive. Termination must be provided by an external source. Similarly, termination power is hard locked to "Drive supplies the Bus" and can not be changed. Although compliant with LVD controllers, these settings may not be fully compatible with standard Single-Ended SCSI controllers.