Lowell Avenue facade. Photo: A. B. Clark, 1920
I received confirmation from two sources that the house was split prior to 1950. Looking at the aerial views on Google Earth, the split appears to have been made prior to 1948.
Green: 275 Lowell, Orange: 1680 Bryant. Aerial Photo: USGS, 1948
This story dovetails with information I received from Rick Simpson, whose family owned 1680 Bryant from 1950 to 1968. He had been told that the passage connecting the two sides of the house had been severed immediately after WWII. Rick clarified that the south portion of the house had the address 275 Lowell Avenue and was owned by the family of concert pianist Adolf Baller from 1950 to sometime in the 1990's. After the Ballers sold it, the new owner tore it down to build a larger house.
Bryant Street facade. Photo: S. Sigurdson, 2003