Welcome to the forums Wyn! The most likely candidate (IMHO) would be an '83/84ish Randonneur although ours came with a more pedestrian frame made from Mangalloy and had a vertical drop. Oddly Bianchis touring offering in that period had flat bars and regular side pull brakes.
Yes I am pretty sure this come from Japan. Are sure about the tubing? The Piaggio decal is the Parent company of Bianchi and for some reason (maybe Italian marketing?) most Bianchis carried that decal through this time period.
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