Factual error: While handling the ignition coil cable to the distributor cap, Joe Pesci tells De Niro that the timing chain needs adjustment in his truck. A truck of that year with an inline Chevy motor would not have a timing chain at all, instead this truck would be equipped with a direct drive timing gear. Even if it had a timing chain, it would be behind the water pump and a cover. It would have been a several hour job to replace, not possible to adjust it.
Continuity mistake: When a man attacks Hoffa in court, Hoffa's son attacks him, then in the next shot he is not up from his chair. (01:22:47)
Factual error: In the movie it says Allen Dorfman was shot in 1979 - he was actually shot in 1983. (00:56:25)
Factual error: When Frank drives up the street looking for the "Hoffa hit house" there is a white 2001 Mercedes van sitting at the driveway beside one of the houses. (02:37:33)
Factual error: When Frank watches TV the news anchor says that Crazy Joe was killed at age 47 - he was 43. (01:47:25)
Continuity mistake: When Frank calls Jo after Jimmy's death Frank has different reactions in different shots. Obviously, the scene is shot more than once and while editing they made the mistake and couldn't cut correctly. (02:52:10)
Factual error: The twin engine Cessna 421C airplane which Frank travels in has modern avionics upgrade not available at the time. Tail number N212RV wasn't issued an air worthiness certificate until June 1979.
Factual error: When the Machus Red Fox is shown, it is depicted in the middle of a country road, with mountains in the background. The actual Machus Red Fox at the time was on a busy street behind a strip mall on Telegraph road near 15 mile. Also, big hills that are shown in the movie are non-existent in Michigan.
Factual error: In the opening scene when De Niro is mapping out his route from Pennsylvania to Detroit, the map shows interstate 275 which wasn't even built at that point.
Revealing mistake: In the shot of De Niro sitting in the plane you can see the controls next to the pilot. We hear the plane start but the pilot never touches the controls. It taxis for takeoff and the mixture controls (red knobs) are still in the mixture cutoff zone. No fuel would go to the engines and they would not run. Also both engines start at the same time, which is impossible with any twin engine airplane. Not to mention that the avionics are all dark as well and the engine gauges read zero. (02:35:00 - 02:35:40)
Factual error: Multiple scenes show cars with Pennsylvania license plates on the front bumper. Pennsylvania did away with the front license plate in 1957.
Factual error: During the trip's second stop for smoking, the overhead wiring has an optic fiber box joint visible, which doesn't fit for that year. (00:21:18)
Factual error: When plotting the trip to Detroit, it show Frank drawing his route as I 80 merging onto 75N in Toledo toward Detroit. Toledo is approximately 60 miles south of Detroit. When actually driving, they stop at a HoJo's and pass a road sign that says Columbus 64, Dayton 86 and Detroit 212 on I 75.That puts them going north on I 75 between Cincinnati and Dayton. That would have put them 160 miles south of I-80.
Factual error: Despite the great effort (and expense) to recreate the 1950s through 1970s with vintage cars, SOHIO gas stations and a HoJos motel, none of the houses in any of the street shots show TV antennas on the roofs or chimneys. It's highly unlikely that every home on a given street used "rabbit ears." Cable didn't make inroads until the late 70s at best.