Ralph Humphrey mentioned it a couple of days ago on Facebook.
Earlier today, the album cover turned up :
They played two shows that night.
Here's data of the first one :
The Mothers Of Invention, October - December 1973
FZ, Napoleon Murphy Brock, Tom Fowler, George Duke, Ruth Underwood, Bruce Fowler, Ralph Humphrey, Chester Thompson.
1973 10 31 - Auditorium Theatre, Chicago, IL
90 min, Aud, B
soundcheck intro, Pygmy Twylyte, The Idiot Bastard Son, Cheepnis, Eric Dolphy Memorial Barbecue, Kung Fu, Penguin In Bondage, T'Mershi Duween, Dog Meat, RDNZL, Village Of The Sun, Echidna's Arf, Don't You Ever Wash That Thing?, Montana, improvisations, Dupree's Paradise, Dickie's Such An Asshole