Loren (Mazzacane) Connors would be an interesting one from an outsider perspective. Massive number of self released records that are thankfully now being collected and re-released. Not sure what state of mind he was in when he recorded the Daggett St records (Unaccompanied Acoustic Guitar Improvisations Vol 1-9) but he literally howls along with his guitar on some of these.
R. Stevie Moore would be another prolific outsider. Albert and Donald Ayler would also spring to mind and Wild Man Fischer.
Robot, i'm guessing you may have had a read of Terry Castle's piece in the latest LRB? If not it would be right up your street.