Looks like it was done after the fact to me. The edge of the chrome strip looks kinda ragged in the photo, which would not be up to Honda production standards even in the '70s.
Does the paint around the bracket look at all different from the rest of the bike? I know that when these bikes were being built, you could go to the Honda shop and buy the base coat, candy color, and clear in fizzy cans. I repainted my old '50 in about 71 that way. Too bad those aren't still available!
Whoever did the bracket did a pretty nice job however, but I would say it is not original. OTOH, if it is an early prototype, gotta be worth some real money, cuz it's gota be rare!