the lugs and crown *might* be Cinelli products, how about a shot of the underside of the lugs? I think the XX on the crown is simply decorative. It's clearly a high-end Italian-made frame given the Campy ends and build quality...but I don't know who or even an exact date, but I'd be surprised if as early as late '50s...more like late '60s to my eye. Stay caps remind me of some Bianchis but...not enough to put it in that column.
Now some details confuse me: those cable guides and that chainstay bridge has a boss for fender mounting...are there eyelets on the forkends? Me thinks it had barcons and fenders, and a frame pump...unusual for an Italian.