Spencer Stone, Alek Skarlatos and Anthony Sadler, who play themselves in "The 15:17 to Paris", were reunited in a cinema in the French capital where emergency services crews who tended the injured after the attack were among the audience.
Some of them also play themselves in the drama which retells how the three childhood friends from California overpowered a Moroccan jihadist armed with an AK-47 on the Paris-bound high-speed service from Amsterdam carrying more than 500 passengers.
"I hope you like the film. We wanted to be exact about what happened," said Skarlatos, 25, an Oregon National Guardsman who served in Afghanistan.
US Air Force Airman Spencer Stone charged at Ayoub El Khazzan after he wounded another passengerand managed to disarm him of the AK-47 and of a pistol which jammed as El Khazzan tried to shoot him.
Stone was slashed with a bolt cutter around the neck as Skarlatos and Sadler knocked the attacker unconscious and then "hog-tied" him.
The three were hailed as heroes both in the United States and in France, where they were awarded the Legion of Honour, the country's highest decoration.
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"I reprised my role as a nurse," said Nathalie Capron, who looked after the injured when the train pulled into Arras station in northern France.
Playing herself made it feel weirdly "less natural", she told AFP after the preview screening for cast and crew in the French capital last week.
The film -- which opens in cinemas in the US and the UK on Friday -- follows the course of the friends' lives, from their childhood struggles to the series of unlikely events leading up to the thwarted attack.
'We could all be dead'
Hollywood legend Eastwood's last two films -- "Sully" and "American Sniper" -- were also about real-life heroes, but this is the first time he has used the real protagonists to play themselves.
The 87-year-old, who makes no apology for his gung-ho patriotism, said he wanted to "make people aware that they have the strength to do (extraordinary) things themselves and I think this story is a champion of all that.
"There could have been a lot of people killed, (the attacker) had a lot of ammunition, he had a very reliable gun." If his young stars hadn't acted it could have been a slaughter, he said in a filmed interview with the cast released to promote the movie.
Skarlatos, who appeared on the "Dancing With the Stars" US television show after the attack, said that "knowing each other since we were very young, it was the icing on the cake that we got to play ourselves.
"If anything went differently we would probably all have been dead," he added.
"Never in a million years did I think that we would play ourselves in a Clint Eastwood movie," said Stone.
"We knew he took a chance on us and we didn't want to disappoint him."