The quadrajet was a four barrel carb. The four barrel carb was the basically the default muscle car setup, a single two barrel was a base model setup, mostly for smaller displacement v8’s (sub 300 cubic inch/ 5 liter) at least untill the carb and cafe acts in the 70’s. in the late fifties you had some factory dual Quads which was 2x 4 barrel carburetors, Chevy did that for the 409 but by the 60’s that was mostly just racers or something that cane packed in the trunk. the tripower, triple deuce, or sixpack setup was more prevelent, but still not as common, it was mostly a trim level or dealer installed option very few engines if any came exclusively with a triple carb setup. The only muscle car with dcoe I know of was the 428 hemi that had a dual setup as a option.