Both Plymouth and Pontiac were relative latecomers to car making, and both were corporate-created brands aimed at a similar market niche. GM created Pontiac in 1926 as a low priced companion brand to Oakland, and Chrysler created Plymouth in 1928 as a low price alternative to Dodge.
btw the movie "AIRPLANE!" was based on was the forgettable 1957 melodrama "ZERO HOUR!" It's apretty hilarious to watch now because you realize AIRPLANE! mostly follows it scene by scene but with added gags. 
*the above illustration was from a 1947 Dodge truck ad. The '30s to '50s were sort of a high watermark for the advertising illustration arts, especially around the holidays. I've been able to find several delightful ones featuring our dimwitted but delicious Thanksgiving dinner guests of honor, like this one for the stunning 1939 LaSalle. Like the turkey, LaSalle had a short lived future; the brand was retired by GM after the 1940 model year.
Enzo Ferrari was still a successful racing driver of Alfa Romeos in 1929, and Alfa had its own in house racing arm, Alfa Corse. But by the late 20s the expense of a factory racing team was becoming untenable and Alfa was wavering on further support.
The Roach Coach, designed by Ed Newton/ built by Dan Woods & Jim Jacobs in 1972-77. Powered by a Ford DOHC Indy engine. Built for Roach Industries of T-shirt and “Odd Rods” sticker fame 
*of course I would be remiss to not mention the Faber homecoming parade car that spurred mayhem at Mayor DePasto's showroom, the Delta Deathmobile. a/k/a pledge Kent Dorfman's '64 Lincoln Continental loaned from his brother. A '64 is an anachronism given the timeline of the movie, but hey, I'll forgive them that.
