(I wonder what ever became of those feedback canceling microphones from the WoS? I don't reckon they'd be good for anything else... come to think of it, I guess they had to be made for The Wall, didn't they?)
Yes. Originally they mounted 2 Sennheiser 421s together & ran them through a solid-state amplification system designed by John Curl & Ron Wickersham and built by Mark Levinson, but by the WoS had moved on to the ones shown, which were two Brüel & Kjær mics built onto a box with the circuitry. (Jackson, Blair.
Grateful Dead Gear: The Band's Instruments, Sound Systems, and Recording Sessions From 1965 To 1995. San Francisco: Backbeat Books, 2006, pp. 139-140)
Peter