The pic is surrounded by a large white border. If you save the file, and edit out the border, the pic can be zoomed and seen quite well.
Itom doesn't seem to have the same frame design.
Some Benelli's seem to have the right frame structure, but can't find a circa 1961 pic of that model - and the tank doesn't quite look Benelli either. (badge looks wrong). Cimati ??
1961 Motorcycle magazines would probably have adverts of them, there can't be too many varieties imported back then ? Does you dad recall the name of the dealer ?