Well, that drew plenty of quick responses :-) - thank you all!
Practically everyone pointed me at
http://www.netbsd.org/Documentation/Hardware/Machines/DEC/lk201.html,
which does indeed contain the info I asked for (which was actually only
a subset of what I'm looking for - see belwo).

One person (who copied the list) wrote

> x2x (ask google) or synergy2 (http://synergy2.sourceforge.net/)?
> These programms can redirect keyboard and mouse input from one
> machine to an other.  The machines need to run X.

I might, except that I don't want this to be X-specific and I would
really rather avoid using another machine if it can be helped.  But
from the sound of it, I will have no problem.

This is good.  It will confuse the ROM selftest, but it appears I
should be able to connect a Sun keyboard with just a level shifter and
inverter, same as for a bog-standard serial port.

Now, does anyone have the corresponding information for DEC mice?  In
particular, the VSXXX?

Also, does anyone have any doc on the drawing acceleration hardware in
the 3000-300X?  I have a document (EK-D3SYS-PM B01) that purports to
describe it, but I haven't been able to make anything but simple
framebuffer mode actually work, so either the doc doesn't accurately
describe the hardware I have or I don't understand it clearly.  I'll
continue experimenting, but more detailed doc would certainly help.

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