The 478 ci V6 was first introduced by GMC for its massive 6500 Series trucks ... Ultimately, both engines were used in GMCs commercial trucks until the early 1970s, when they were replaced ...

The big-block V6 was made from 1960 to 1974 for GMC's 6500-series commercial pickup trucks, and it is still one of the biggest V6 engines ever produced. The big block wasn't a tower of power ...