The Mabreys as Baptists, said a commonly used Catholic grace before a meal. In that period of the 1950s, no Baptist would use a Catholic prayer.
The takeoff of the Lockheed Constellation was inconsistent with flight characteristics of the Connie, or other propliners of the day. The plane took off, rotated, and climbed at a 30 degree angle. This was not an F-14 jet fighter, folks. That airplane's rate of climb was about 1/4 that of a jetliner, whose power to weight ratio was much higher.
When Marla is eating her meal, she uses her fork and knife and in the English way, by using the knife to push food onto her fork. She's supposed to be from Virginia.
The Steve Coogan character, Colonel Nigel Briggs, wears the uniform of (at least largely - the shoulder insignia are absent) an RAF Group Captain. There is no rank of Colonel in the RAF - though the British army rank of Colonel is equivalent to Group Captain in status.
In one scene, Howard and Harlan discuss the fact that Marla is the only RKO contract girl with the initials MM. Later in the film, however, we learned that Mamie's last name also begins with the letter M.
The H-4 Hercules, aka, "The Spruce Goose," actually flew its one and only flight on November 2, 1947, well before the events of the film.
Throughout the 1958 scenes, Frank is driving a 1961 Chrysler. Hughes wasn't that rich.
This is supposed to be 1958 when Frank drives to Las Vegas, yet the marquee on Wilbur Clark's Desert Inn says "Lou Walters All New 1955 Latin Quarter Review".
The movie begins with a "1964" dateline and later has a "five years before" card on screen. At one point, a radio broadcast informs listeners that the Brooklyn Dodgers will soon be moving to Los Angeles. By 1959 they had already done so and in fact played the Chicago White Sox in the World Series that year.
Although supposedly set in 1958, Hughes' is shown crashing the XF-11 prototype aircraft, which actually happened over a decade earlier, on July 7, 1946.
When Frank first drives Marla and her mom, they travel east on Hollywood Boulevard, passing the Egyptian Theatre on their right. A few seconds later, the Chinese Theatre goes past on their left. They should have passed the Chinese Theatre first.
Howard Hughes was married to Jean Peters from 1957-1971 so was not single and needing a wife to keep him out of the loony bin as purported in the story line.
In a conversation with Marla Howard refers to "a couple of limeys" who worked out DNA. Watson and Crick did their work in England, but Watson is American.