Hi there
I've found 62 South Molton Street listed on the 1901 Census, but unfortunately the property was uninhabited on the night the Census was taken. Reference: RG 13/81 folio 7 page 5.
Going back to the 1891 Census, the property was occupied by a widow, Ellen Warren, with her son William and seven other young women who were variously described as dressmakers, milliners, and saleswomen. Reference: RG 12/67 folio 40 page 30
It looks like 62 South Molton Street - and several adjacent properties - were redeveloped and/or demolished not long after your great-grandfather's birth. An advert in The Times on Tuesday February 12 1901 (pg. 16; Issue 36376; col D) announced the forthcoming auction of the "building site...now occupied by 57, 58, 59, 60, 61 and 62 South Molton Street...No.57 being the Globe Publichouse." And then there were a number of adverts in The Times in the 1950's for The Triangle Secretarial Training College with the address 59-62 South Molton Street.
Hope this helps.
Dave