The sixth-generation Ford F-Series was introduced for the 1973 model year. Known by enthusiasts as the "Dentside," the F-350 was based on the one-ton chassis, whereas the F-250 was based on the 3/4 ton chassis. The F-350, a new model series for 1973, was offered as a regular cab, a two-door Supercab, and a four-door Crew Cab. A Styleside long bed was the only available option, and the majority configured in two-wheel drive, with 1979 being the only year with a 4X4 drivetrain. The F-350 featured an extended wheelbase chassis; however, they were the same overall length as an F-250. Engines offered were a six-cylinder 300cid, and six V8's throughout the years, 302cid, 351cid, 360cid, 390cid, 400cid, and 460cid. Transmissions offered were automatic, three-speed, and, later, a 4-speed manual depending on engine and drivetrain. For heavier duty tasks, axles, frame thickness, and springs were larger than the F-100, F-150, and F-250. This added to the F-350 having the greatest Gross Vehicle Weight Rating of nearly 10,000 pounds. All models could be outfitted with any three available trim levels, including the entry-level Custom, mid-level Ranger, Camper Special, Super Camper Special, or top-of-the-line Ranger XLT and Ranger Lariat. For 1978, square headlights replaced the previous models' round ones on higher trim package models, such as Lariat and Ranger, and in 1979 became standard equipment. 1979 would also be the last year for Sixth Generation production, with the Seventh Generation F-Series replacing it.