For comparison, here are three of the "contenders".

Shure Slim-X 777

Monarch MC-24

Shure 535
Here are some of the photos of Little Walter from the gig:

Mic cord looped back and taped with electrical tape to body of mic

Note smooth chrome "head" of mic, with no rings like a Shure 535 and no notches on sides like Monarch

Compare shape of head of mic to Slim-X.

Note overall shape, size and color of mic, compare to Slim-X

Note mic cord looped back and secured to body with black tape, also connector.

Compare the screw on the side of the "head" of mic to Slim-X, also note Switchcraft-type screw on, spring base connector. Compare size of mic to size of harp
Note that the Shure 535 is 7 23/32 inches in length not including the cable connector, which appears to add at least another inch, making it approximately 8 3/4 inches long minimum. Also note that the concentric circles around the "head" of the 535 are not present on this mic.
My conclusion - it's got to be a single Shure 777 Slim-X, or a Japanese carbon copy of one.