I had the same thoughts given the amount of rust. Mine is a Superissimo version. Clean it up and ride it to determine fit and rideability.
I appreciate your pictures as there are a lot of variations in Colnago frame features. I have yet to see a SN on any Colnago of this vintage. Mine has a 53 on the DS RDO and USA on the NDS RDO.
Are those GL330 rims? Interesting to see the LF record hubs. Mine came with GL330 and Mavic 501RD's. I went OCD on pic of mine. they are here if interested:
http://s985.photobucket.com/albums/ae332/SJX426/