Mark -
I'd to see the pix, if you'll send them off-list. Sounds to me like what you have is some sort of a one-off aero experiment, which a lot of builders were experimenting with in the early-to-mid 80's. The shifters mounted on top of the down tube, with the cables routed internally, point specifically to this time frame. The reduced headset/headtube may have been some sort of attempt at a smaller front profile. Likewise, smaller diameter tubing might explain the "double-socket" BB. Just guesses, of course. Pix may tell more , and the Colnago experts on the list will probably provide better info.
Wayne Bingham
Falls Church VA