From Corry Arnold:
"The most complete line-up I've been able to assemble is the following:

Doug Sahm (Guitar)
Jerry Garcia (Guitar & Pedal Steel)
Phil Lesh (Bass)
Jerry Barnett (Drums . Shiva’s Headband)
Leon Russell (Piano)
Mary Egan (Fiddle . Greazy Wheels)
Benny Thurman (Fiddle . 13th Floor Elevator bassist)

Though he was in attendance that evening, there is no verifiable evidence that Bill Kreutzmann sat in with the band. When asked a few years ago the owner of the Armadillo seemed to recall Bill feeling sick that night."

http://www.tapecity.org/showthread.php?t=6899

This fits my ears, and fits the evidence. There is definitely a picture of Phil playing bass, but it didn't sound fluid enough for Phil and Bill. But Phil and a local (if talented) drummer fits what I heard. I'm willing to go with this lineup, so you may want to revise whatever I wrote.