Aha! The smoking gun has been found.

Step right up folks, it's "test your knowledge" time.

To recap:  Old van with 150k miles, was running fine, suddenly lost
power and wouldn't start again, about 10 miles after a fillup.
After towing to a gas station started once, then immediately died
after about 1 second.   Sounded normal when it cranked.    Wouldn't
start again.

At first, thought a hall sender problem, replaced distributor and re-
aligned the distributor gear which was installed improperly by the
PO.  This turned out to be a red herring.

Afterwards, still no spark on the #1 plug (as measured by a timing
light on the #1 spark plug wire).  Spark observed, however, when
connected to the wire between the coil and the distributor.

So here is today's super stumper question:

Why would there be spark at the coil wire, but not on the #1 spark plug?

20 points if you get it here.

Hint 1: It's NOT one of the obvious answers:   The Distributor, coil,
hall generator, hall sender, and all wiring is new and functional.
10 points if you get it now.

Hint 2: Although the #3 spark plug looked a bit black, it was in
otherwise good condition.   I had not as of yet pulled the #1 plug.
5 points if you guess it now.

See here for the smoking gun:   http://xochi.com/vanagon/Plug1.jpg

So for the next question, what happened to cause this?