Measure the seatpost diameter. If the (presumably) 28.6mm OD seat tube takes a 27.2mm post, you have a butted frame, probably CrMo. A 26.4mm post indicates straight-gauge moly steel, whereas anything smaller suggests cheapo carbon steel.
On a 1970s bike, cottered cranks are definitely a low-end marker, but remember that the 1961 Schwinn Paramount came with cottered cranks and Weinmann centerpulls, as did both of my otherwise high end ca. 1960 Capos.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069