Interesting Bianchi. I can't help you witht henumbers but I do think that headset post dates the frame for a few years. The decal on the seattube seems to suggest late 70s to me. More pics?
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk