There are a few record companies left that continue to restore and release old archive recordings in high quality sound. Richard Caniell`s Immortal Performances in Canada is one. I strongly recommend Roméo et Juliette (IPCD 1003-2) and Verdi Requiem (IPCD 1073-2)and a NEW release is due in April/May 2019 (IPCD 1110-2 Manon Lescaut 1959 + bonus concert recordings).
"Björling on Pristine Audio and Immortal Performances,"
Journal of the Jussi Björling Societies of the USA & UK: Vol. 27
, Article 10.
Available at: https://scholarsarchive.byu.edu/jussibjorlingsociety/vol27/iss1/10