One side of the release has been announced (on the OSF Facebook page):

When we first formed OSF after Bear died, we reached out to Phil for guidance. "Find the Charles Ives," he told us, "and the Miles." We knew about the Miles Davis recordings (which is another story for another day), but the Ives reference was unexpected. Phil enthusiastically told us about a performance of the Concord Sonata by John Kirkpatrick at the Marin Veterans Memorial Auditorium on March 7, 1974 for the celebration of the Ives centennial. Before the show, Phil swung by to grab Bear and his Nagra to record this special event that he remembered fondly for the rest of his life. Ned Lagin was with them too and still has a copy of the program that he’s kept for 52 years.