So has anyone actually contacted the new owner of DB's business, or his widow, or his inheritors? Shouldn't this be the first step?

AND meanwhile the tapes are likely disintegrating ...

http://www.vox.com/2014/10/13/6840233/music-archiving-disappearance-history

Luckily the technology now exists to lift recordings from vinyl.

I advise everyone or anyone to join the 'Association for Recorded Sound Discussion List' at

They debate such issues and the archives are a goldmine of hints and tips and experiences about preserving audio recordings. The List is sponsored by the LOC in Washington. Many members are professional archivists with considerable experience at rescuing or restoring audio recordings.

CJB