Measure the width of the BB shell. 68mm = Japanese Bianchi, 70 = Italian. As Luker observed, the latter is considered more collectible and more valuable, but either should be fine. Bianchi made several grades of frames, and you want at least a double-butted moly steel main triangle.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069