I just stumbled across some specs to a 1984 Allegro which match yours with the following exceptions: Ofmega Competizone crankset, San Marco seat post, Selle Italia saddle, Weinmann 605 brakes. The cranks and saddle may be match, with Bianchi simply having contracted the respective companies to label them with Bianchi. The specs even mention the "engraved "B" top eyes and fork crown". Given the serial number, I suspect your is a 1983 model as John E. suggests.
BTW, the 1984 model's tubset is Columbus Aelle, throughout. I suspect yours is the same. MSR was $499.00 US.