OHV unit for the wagons with higher compression and . There were few changes for 1961: the Superba Special was renamed to the Marathon and model codes for 1961 and 1962 were W/10L (sedan) and W/A10 (wagon) instead. 1962 was the last year for the A10 model codes. Wagons came standard with a motorized fold-down rear seat, which — combined with different bodies — pushed the price $350 above the sedan. Three-on-the-tree manual shift was standard, and a Borg-Warner three-speed automatic with optional overdrive was an option. In 1963, model codes switched to A12 (sedan) and A12W (wagon) and a long-wheelbase limousine (the Marathon Town Custom) was introduced with model code A19E, riding on a wheelbase extended to . The high-compression OHV 6 was made optional for all vehicles. For 1964, which was the last year for the Continental 6, the Superba name was dropped and the Town Custom model code was revised to A12E. Some of the 1964 Checkers were revised later to be part of the 1965 model year if their serial number was higher than 20000. This also was the year that Chevrolet engines and transmissions were offered; the standard engine was the "Turbo-Thrift" 230 I-6 and the optional engine was the small block 283 V-8; an optional 2-speed Turbo Hydramatic could be specified as a $248 option instead of the standard 3-speed Warner Gear manual transmission. A second engine option, the small block 327 V-8, was added for 1966. The A12E extended-wheelbase sedan was dropped for the 1967 model year, but presumably was available as a special order as Aerobus production continued. Starting in 1967, an energy-absorbing steering column was fitted to meet safety regulations, similar in appearance to AMC's column. Round side marker lights on each fender were added in 1968. Seat belts were fitted as mandated by the United States government, including shoulder belts on Checkers built after December 1967. The 1969 cars got high-rise headrests and 1970 models adopted the government-required steering column and shift lever lock. The 1974 Checkers eschewed the attractive, chrome-plated bumpers for girder-like, aluminum-painted units. The 1975 models featured the catalytic converter emissions device, which came with an "Unleaded Fuel Only" label for both fuel gauge and fuel filler. During the 1970s, Checkers adopted a standard Chevrolet steering column assembly, including steering wheel (without the "Chevrolet" badges), shift lever and ignition switch. The 1978 and later models can be