Caul lived in the 3-story Sylvia Apartments at 700 Laguna Street, on the corner of Grove in the Hayes Valley section of the Western Addition (map). Here's a recent photo of the front door.
Then ... Caul lets himself into the apartment building. No iron security door back then.
... and Now, It's been 40 years but it's still the same old lobby.
Then ... Upstairs on the second floor corridor he has just passed apartment 206 on his left, 208 is on our left and he is heading for his apartment at the end of the corridor, # 207, just off the right of this picture.
... and Now, the same corridor no longer has a molding strip along the upper walls and the light fixtures and doors and casings have been replaced. It was a little classier then.
Then ... CitySleuth composited several interior shots to come up with this overall panorama of Caul's apartment, created by combining apartments 206 and 207 into one unit (click image to enlarge). The 207 entrance leads from the corridor into the apartment from the far right and the two bay windows on the left wall look out directly across Laguna. The building seen across the street at far left was being torn down as this scene was filmed, coinciding with the tail end of the Western Addition 'urban renewal' program that saw the demolition of 2500 Victorian homes.
... and Now, street views from interior scenes led CitySleuth to conclude that the apartment was on the second level, highlighted in red. The building was built in 1928 and was mostly vacant when Coppola filmed the movie but it survived the demolition taking place all around it. Birch Street intersects on the left.
Then ... The kitchen is at the corner of the building and its west view looks across Laguna along Birch towards apartments on Buchanan Street.
... and Now, Here's the same view today taken from street level; those same apartments in the distance are still there, the matching top story can be seen above a newer building. The apartments directly across the street on the left replaced those seen being demolished in the movie.