I think the headbadge decals started in 1970. The high flange hubs look original, crankset looks like late 70's or later. Can't really tell about the brakes, my 74 Gran Premio came with Universal sidepulls as did most 70's Legnanos. If you think the components are original that might help you date the bike. Also, Classic Rendezvous has a page in their Legnano section that references some serial #'s.