Mike,

Playing in G, I do

G G7 C Eb

for the decreasing sequence.

Play the C as 310233 ( high string to low) and just slide up 3 frets and you'll have the Eb. You can skip or damp the bass string if you need.

Alternatives to the Eb are Cm (X1013X) and C#dim (3232xx) (I think.) I forget what van Ronk plays.

So the song is
G D7 Met a girl..
G D7 Said...
G D7 A7 D7 I never..
Again for second half of verse. Then
G E7 A7 D7 That'll...
G E7 A7 D7
G G7 C Eb The descending part Hmm Hmm..
G E7 A7 D7

Good luck. Play with it some. It's a blues, after all. (Damn ggod one too)

T.J.