For 1970s Salisbury axles: Castrol do both an EP90 in their Classic range and for lim slip axles LS90 is still available though now renamed as AxleZ LS90. Both are as the original listings by Morgan and Salisbury, why are you thinking of something different.
At a personal level I’ve happily used LS90 for the last 150,000m; however whether it’s better or worse than any other specified oil
would have been, I’ve no idea.
