The poster for East of Eden (1955) shows a picture of James Dean in his famous red jacket with the white t-shirt and jeans from _Rebel without a Cause (1955)_, a movie which came out on a later date.
When the Chevy convertible is being pulled out of the water, you can see by the grille it is clearly a 1953. For the rest of the movie, it's a 1954 Chevy convertible.
The early 50's Chevy the guys are working on that belongs to Spider, shows an 80's specific steering wheel mounted on it, as this is supposed to be a 50's movie.
In the last scene, when the guys jump the 54 Chevy and the parts fly off, there are 80's model vehicles parked down the street. Most notable, is a "new" car parked behind the 56 Chevy on the left, almost as if it was an afterthought to hide it.