AFAIK the biggest diff would be the forkcrown: SC would have the signature full-sloping crown but a "B" would have a flat crown (according to the Cinelli Timeline: 1950 to 55 – Modello B with flat crown and internal rear-brake cable routing.)
BTW until 1960 the "SC" stood for "Speciale Corsa" but after then became "Super Corsa"