You're not the only one having a hard time telling a Mexico from a Super. Check out:
http://sheldonbrown.com/vrbn-a-f.html#colnago
Masters use the shaped Columbus "Gilco" tubing and should have a Columbus decal identifying the tubeset as such. The tubes are not crimped but rather drawn in that shape by Columbus.
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“Life is not one damned thing after another. Life is one damned thing over and over.”
Edna St. Vincent Millay