What's the crank length on the Bianchi? What's your inseam and standover clearance like? Just wondering if the Bianchi really is too big for you. A shorter crank would help it fit, unless the frame is too long for you.

I see no problem at all in taking the Campy parts off the Bianchi. Major issues have been mentioned. I think the cable stops on the Bianchi will bolt right onto the down tube shifter bosses on the Nishiki. The Nishiki might take nutted brakes, while the Campy will be recessed. You could keep the Nishiki brakes that are on there. As well, keeping the BB that is in the Nishiki will work if the Campy crank uses the same taper and the spinde length is OK. Otherwise you can use the crank that is on the Nishiki until you get a BB to fit the Campy crank.