As Alden is leaving for Vietnam, it is supposed to be Easter weekend of 1969. The kid on the bus is reading a book with the Brady Bunch on the cover. The Brady Bunch didn't premiere until September of 1969.
When we are first shown their town, there is a yellow 1977 Mercury Marquis parked on the left side of the street facing the camera.
The bus Alden gets on says Palmetto Tours on it. It would not be in Maryland, where the film is supposed to take place. South Carolina is the Palmetto State.