[GRC]

Do you NEED to do anything with it?

Why not keep it in clean, dry conditions and really take your time over finding someone who really wants or needs it? It sounds like it could be real 'treasure trove' for someone like your father-in-law. Have you considered whether or not the Met might be interested? There may be performances in there that they've considered lost for years, by artists who may have passed away long ago...... There may be record labels that specialise in this. If you're feeling business-like, you may have the starting point for your own record label.

You could, of course, transfer it and torrent it here. mdshrk1 has made a vocation out of jazz and classics here.

Would you have the time or the inclination to transcribe the record cards into a format that could be circulated to interested parties? Word doc, text doc or similar?

It would also help others if you had some indication of what speed they were recorded at, what track config they have (2 or 4 track), what size of reels they are on, and crucially - what tape type. There's serious issues with Ampex tape of a certain era, and you may find these to be unrecoverable