Used frequently in films for generic taxi cabs, Checkers were basically the same from 1958 through 1982. However numerous small changes identify specific years. In 1958, Sam's Checker Marathon taxi cab has a "V8" emblem, indicating that it was built after 1964, since all Checkers built before then had six cylinder engines.
The plot is set In 1958. After Sam "revives" Angela and is driving her to the taxi dispatch office, she advises him to turn right; a 1978 Ford Fairmont can be seen parked at the curb.
When Sam first leaps into the taxi driver he looks at his reflection in the car's side mirror. From the driver's point of view, the mirror would be angled to show the view of the side and rear of the car, a person sitting normally in the driver's seat would not be able to see their reflection in the side mirror.
Early on, as Al is (mis)guiding Sam in the cab, Angela tells him to take a right, which he does. The scene is set in in 1958, however, the background includes many modern elements, including an early 1980's station wagon, a modern skyscraper, and a very telling AAA neon sign.
Although this episode takes place in May 1958, the May 18, 1959 issue of "Life" can be seen on Frank O'Connor's desk.
At the end, Angela calling Sam by his name is supposed to prove that she is his guardian angel. However, at least once, Al called Sam by his name in Angela's presence so she would know him by that name in any event.
(at around 43 mins) Al passes Lenny (Max's dad) and knocks his shirt, it can be seen wafting open as he passes; being a hologram he should have passed straight through it.