For the vast majority of the B-series' life span, GM's medium duty conventional trucks were based heavily upon the design of their full-sized pickup trucks. While the chassis underneath was of a unique design, the cab and some of the outer bodywork would be derived from the full-size pickup trucks. The B-series, as a result, closely resembled GM's pickup trucks from the 1950s, up until the mid-1960s. In 1966, GMC introduced its own version of the B-Series, unrelated to Chevrolet.