Christine is said to be a 1958 Plymouth Fury, which had similar panels and trim to the 1957 model. When the Fury line was introduced, it was essentially a sport and trim package on the Belvedere - notably with two doors, gold anodized trim, gold grille and dual four-barrel carburetors. Christine, as shown in the movie, could have been any two door Belvedere with a 318 or 350 engine. Although over 5300 Furys - and far more Belvederes - were built in 1958, they have since become very rare and are now collector's items. There were between 13 and 16 (depending on source) Belvederes/Furys smashed in the making of the movie (out of the roughly 25 used), but it is unknown whether they were 1957 or 1958 models, or a combination. In any event, Plymouth enthusiasts were infuriated, although the movie popularized the car and probably saved many of them - in the same way that Back to the Future did for the DeLorean. In the original Stephen King book, the car had four doors, but this was changed to a two-door model when it was realized that there never was a four-door 1958 Plymouth Fury. Although all 1958 Plymouth Furys had Buckskin Beige exterior paint and gold anodized aluminum side trim and grille, the book mentions that this particular car was custom ordered in Ford red.
SPOILER: When Arnie first brings Christine to Darnell's Garage, he walks back to Dennis' car and asks him to honk his horn. In the background, the bulldozer that will be used to destroy Christine can be seen.
SPOILER: After reading over the book, actor Keith Gordon (Arnie) and the costume designer came up with a visual way to show Arnie being possessed by Christine. As the movie progresses, Arnie begins to wear clothes that reflect the era of Christine's make. At various points, especially when Arnie is yelling at Leigh on the phone, Arnie is seen wearing button up shirts open with black t-shirts, black pants, and boots like a 1950's "greaser". When he's talking to Junkins (both times), he's wearing a leather vest over a button up shirt (a nod to western TV shows which were popular in the 50's), and he even starts to wear a red suede jacket like James Dean in Rebel Without a Cause.