George,
I'm not a Colnago expert--but I'll give it a shot.
"52" should be size, measured c-t-t, Colnago style.
You have the earlier BB with braze-on cable guides--not the later investment cast, so pre mid-80s. Still have the club cut-out--maybe a bit earlier rather than later [Don't know when they stopped this]. Double bottle braze ons, under BB cable routing--early 80s. [Allen bolt brake bridge and front fork--?? don't actually know when this happened...]
Fork crown is a more modern style than the mid-70s (yours has the small cut-outs on the side)--if you look at Mark Bulgier's scans from 1988-there is a Super Chorus (#16) that you can see your style of fork that stayed pretty consistent on the high-end Colnagos all the way through the Tecnos. Possibly this fork is newer than the rest of the frame...
Rear stay attachment (with the blunt end plugs, not concaved like early 70s) & engraved also suggest late 70s-early 80s.
I'm inclined also to say that it is a early 80s Super--still has the classic 2 braze on cable guides on TT, and the robust round brace between the chain stays. I've seen them with "Super" engraved on the chainstay (mid-70s as in Mark's first "Colnago) catalog) and I've seen them decalled the same (used to have a late 80s/early 90s Super), but I've also seen them plain.
Dean (missing my Colnagos)Kernan
Pomona, New York USA