I've just looked out an old OS map and a modern street atlas. The parapet, bottom left in your dad's picture, is indeed the edge roof of the Ansells buildings fronting on to Upper Portland Street. Park Road ran roughly where the Expressway is today, but at a slightly different angle, as it joined Aston Cross and the tower of Aston Church in a straight line, whereas the expressway runs west of Aston Cross and East of the church. They made such an elaborate junction at the Victoria Road Crossing that it would have been well nigh impossible to link it to Upper Portland Street, so the latter was made into a cul-de-sac off Lichfield Road, and it now known as Portland Street.
Peter