I ran into Will Scarlet last night at Ashkenaz Dead Night where he is a sometime attendee & it finally occured to me to ask him about the "Anderson Theater 11/23/70" Hells Angels Benefit, since he plays harmonica on the Uncle John's Band.
He clearly remembers the gig, as a Hells Angels Benefit, & remembers playing on the Uncle John. He is absolutely positive that this gig WAS NOT at Fillmore East. I asked him if it was at the "Anderson Theater" and he says he doesn't remember the name of the hall but he is certain it wasn't Fillmore East.