1978 GMC 3500 with a 6BT Inline-Six 1978 GMC 3500 crew cab with a Cummins 6BT inline-six " data-medium-file="https://engineswapdepot.com/wp-content/uploads/2020/12/1978-GMC-3500-crew-cab-with-a-Cummins-6BT-inline-six-01-600x450.jpg" da...