The only references to this place (or at least to a slightly fictionalized version with "the words 'Shakespeare Flats' engraved in reddish brown marble over the doorway" and located a block farther south, on 122nd Street) I can find on the internet are from a book entitled Mister Satan's Apprentice: A Blues Memoir. A favorite excerpt:
Later, back in Harlem, we sat in my car in front of Shakespeare Flats and finished off the pint of Romanoff vodka we'd poured into three clear plastic cups. We looked like victims of genital elephantiasis, front pockets bulging with bankrolls and change. Giddy is putting it mildly.