The seat collar/stay tops is definitely Bianchi from the 70's. I have seen those X cut-outs before but cannot remember where. But the raised B in a circle would put it mid to late 70's. The braze-on's (TT guides, and bottle bosses) were most likely not original. Odd as Bianchi's from this period usually had studs brazed on for the bottle bosses.
The rear drop out attachment and the bend of the forks look like that of a higher end model, but the head lugs look right out of the box un-filed. Chrome on the crown was not common for 70's Bianchi's, and they usually had the same raised B on the crown top. So maybe not the original fork?
Maybe somebody will recognize the X cut-outs. Again, I know I've seen those before, just can't place it...
Are you in Europe?