It looks like I was able to answer my own question -- turns out to be
a CTFDF problem (Call The Fine Digital Folks).  For anyone else interested,
the part number is 17-02008-01 (BC56H-03), and DEC will sell you one for
$50, or Seacoast Digital will sell you one for $35.

>  I had basically got around that
> problem by a hack: I had a 50 pin centronics female connector wi about 45
> cm of ribbon capped off with a 50 pin Berg female connector.
[...]

I thought about doing something similar, but for two problems.
My particular VS3100 has the SCSI/ST506 card in it, so I already only
have one SCSI bus, and I really don't want to mangle the case in any
way :)  I guess I'm too much of a purist.

OB-NetBSD/vax:  Lacking, as I do, a serial terminal for a console, I'm
curious to know how much support/hacking has been done to support at
least text-mode video on the VS3100 for console.

Also, any news on when 1.3.1 will be out, and a very short/quick rundown
on bugs squashed/enhancements made?  Thanks much :)

-Seth