Ok, I took another look at the power supplies.  The box with the power cord
is just a filter/switch/distribution point.  Switched three phase power is
available from the round connector on the front of the box.  Now, what I
know may be specific to my VAX, a 6310.  The cable that connects the round
connector to the `power & logic box' has only six wires, two from each
phase.  There are a number of other connections available on the round
connector, which leads me to believe it's a standard part for anumber of
different power schemes.

Here's the fun part!  Inside the `power & logic box', all three phases (
no neutral!) follow a simple path thru a 20A 600V fuse, and then into a
full-wave bridge rectifier, DEC part number 11-26520-01.  A couple of MOVs
offer some protection from transients, and yet more filtering.  

Now, the good news:

It should be possible to simply apply 220 volt single phase (common dryer
power) to any two of the hot wires on the three phase plug!  No neutral is
needed for the computer itself, altho any accessories plugged into the
lower power-distribution box will need one.  These pose a small problem in
that they are connected to different hots to more evenly balance the load
on the three phase supply, but worst case they can be easily tied on to
one phase inside the box-- best case don't use them!

I'll be making a cable to replace the factory assembly, and rewireing the
distribution box to single phase, I believe.  It should be 100% reversable.

Geoff, I'll take some pics for you if you like.  I haven't verified
anything with a meter, but it seems to make sense, and I'll know for sure
one way or the other in a week or so.

ja ne

Bob