Glued on head badge knocks it out of the '70's. N being the first character in the serial also takes it out of the late '70's, and puts it firmly in the '80-'82 4XX or 6XX range. The lack of braze on cable guides would also seem to follow the '80-'82 4XX-6XX line.
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My bikes: '81 Trek 957, '83 Trek 720, '84 Trek 770, '85 Centurion Cinelli