I'm afraid I've never heard much about Salisbury Mansions and can't help.
One thing though, I think the name Salisbury Mansions indicates that it was definitely a lower middle class/middle class development, rather than for yer' working classes.
The working classes tended to live in houses and above shops that were generally split up into rooms rather than flats. Even houses on the ladder and in the Gardens were often dual occupancy, making today's worries about that sort of thing seem out of place. That's what they were built for.
Grand Parade and Salisbury Mansions on the other hand, were purpose built flats and designed, I think, for the families of white collar workers.
Even in my childhood, "Mansion Flats" were considered to be a cut above the rest.
I had a friend who lived in "The Mansions", I lived in Harringay Road, probably late 50's era.
I remember The Mansions as being dark, dingey and unwelcoming. And having a musty sort of smell. I really didn't enjoy spending time visiting him there. But probably not all flats/occupants shared those characteristics. Don't think I ever visited the loos while there so can't comment on that aspect. But certainly not an endearing memory.
Must say now though, from the exterior, they look quite luxurious in comparison. Somebody has done a decent job on them.