Don't ask how I stumbeled across this today.
Purely by accident. But yeah, I was there.
https://www.themckenzietapes.com/tapes/
Also...
I was not at that Maxwells Black Flag show (I believe aquaman was there)
But you will hear, why 'Retired at 21' was such a good opener and the tracks from 'In My head sounded so much better live than on album.