FBI agents Groff and McCallany give their inmate interviewee (Monte Rissel) a 6-pack of Big Red soda. When Rissel opens a can, it has a stay-on-tab, not common until the early or mid 1980s. In the 1970s it almost certainly would have been a pull-tab (aka ring-pull) can.
At the Virginia state prison parking lot, two Ford Econoline vans are in shown in the background. Both have a blue Ford oval badge in the center of the grill, and rectangular headlights. Ford vans used round headlights until 1978-79. The blue-oval logo didn't appear on Econolines until 1983 -- in this time period (1977), prominent chrome 'FORD' lettering was used on the hood.
At the bar (15:40), a red neon sign for Budweiser beer is in the background, with a prominent white cursive ''Bud''. The cursive ''Bud'' was not used until the 1990s. In the 1970s, the sign would have had ''Budweiser'' in plain-block lettering without cursive, or just the plain polygon shape.
When the agents walk out to their car outside the prison, the boom mic is reflected in the car.
There is no way that Holden doesn't get a severe whiplash from the accident.