I know the tapes Pat refers to. I have had a few 'circulating copies'...(i.e., lending library) copies in my care when I was FSGW (Folklore Society of Greater Washington) archivist a number of years ago.
These are/were decent reel-to-reel tapes of 'most' events in those years. I have no idea what condition they are in now, as bleeding and deterioration happen at different rates in various conditions. I know they were stored under reasonably careful conditions for many years by a competent sound engineer, but the only way to know is to check them and attempt to copy them....all the while abiding by copyrights & restrictions.
I do know that there ARE valuble resources there, and that it is a worthwhile project to preserve the performances...if competent volunteers can be found.