From Bill Toboldt. Fix Your Plymouth. All Models 1967-1952. The Goodheart-Willcox Co., Inc., 1967.
According to Wikipedia, the brand lasted from 1928 to 2001. "The inspiration for the Plymouth brand name came from Plymouth binder twine, produced by the Plymouth Cordage Company, also of Plymouth. The name was chosen by Joe Frazer due to the popularity of the twine among farmers." Bizarre.