A 1960 magazine advertisement for the GMC V6 and V12 gasoline and diesel truck engines, touting their cost savings.General Motors has been putting V6 engines in its cars and trucks for more than 65 years, and its very first ones were members of the truck-only GMC V-6 family. Available in displacements from 305 to 637 cubic inches (and a mighty 702 cubic inches for the 12-cylinder Twin Six version), the 60° cylinder bank angle made it easier to squeeze into smaller truck engine compartments. Production continued through 1974 and included diesels and V8s. Here's a beautifully illustrated two-page magazine advertisement for the GMC V-6's debut.