By Mekeisha Madden Toby

“Green Book” is an improbable dream come true.

The entire project could easily have died on the vine. So much of it was unlikely: The friendship between refined pianist Dr. Don Shirley and Tony Lip, an Italian-American bouncer with antiquated views on race; the pairing of comedy director Peter Farrelly with a period drama; and the very concept of a story about the bond that forms between a brilliant black musician and his loquacious white driver navigating the racially segregated South as the Civil Rights movement was nearing its peak.

Then, once in production, Viggo Mortensen had to gain over 50 pounds to play the chunky driver while Mahershala Ali worked with “Green Book” composer and piano virtuoso Kris Bowers in order to convincingly embody the mannerisms and poise of a classically trained musician.

Yet here is “Green Book,” nominated for five Academy Awards® including picture, original screenplay, actor for Mortensen, supporting actor for Ali and film editing for Patrick J. Don Vito.

The film is a passion project that sprouted from anecdotes Anthony “Tony Lip” Vallelonga told his son Nick about his tour of the South with pianist Don Shirley during the early 1960s. Nick enlisted Brian Hayes Currie to help him write the story as a screenplay. Currie, in turn, mentioned to his friend Peter Farrelly that he was working on a script about his friend’s father, who’d chauffeured a Carnegie Hall-dwelling black musician below the Mason-Dixon line with the help of a guide that told African­American motorists which restaurants and hotels would accommodate them.

Farrelly was intrigued. “I just kept thinking about it,” he recalls. “For a month, two months, I’d be lying in bed and think, ‘God, that’s a good story.’ I’d be driving along: ‘Man, that’s a good [story].’ ” Finally, he asked Currie if he could help write it.

Tony Lip had left hours of taped interviews with his son, writer and producer Nick Vallelonga, as well as the letters he had written home to his wife Dolores from the trip. It was great fodder, but there was much work to do. “The hardest thing making a movie by far is writing it,” says Farrelly. “Once you have a script people want to be in, it becomes way easier for me. But it’s because you’ve done that really hard work by writing a script that pulls in a Viggo Mortensen, a Mahershala Ali, a Linda Cardellini [as Dolores].”

When Mortensen read the script, though, it wasn’t an easy sell. He had a long talk with Farrelly about whether the role was a good fit for him.

“I just wasn’t quite sure I’d be right for it because I hadn’t played a guy like this,” Mortensen says. “Part of it was that I was afraid I wouldn’t do justice to the character.” Paradoxically, those concerns ended up helping prod him to take the role. “Whenever I end up doing something, if it’s something out of choice, creatively, it’s maybe always an element of fear involved.

“Even in our first days of shooting, I was still a little worried,” he adds with a laugh. “But once we got going, I got more and more comfortable.”

Ali, though, was enticed by the script’s unusual blend of comedy and drama. “Peter Farrelly, Brian Currie and Nick Vallelonga just so perfectly sculpted this script. They really struck a beautiful balance,” he says. “They pull you to the heights of laughter, and bring you to the depths of someone’s struggle and their pain. I don’t think it ever leans one way or the other too much, so it’s hard to compare to other other projects.”

As it happens, Mortensen and Ali had met when both were up for Academy Awards® ­— Ali for “Moonlight” and Mortensen for “Captain Fantastic.” Mortensen recalls their first encounter: “It was at one of these sort of cocktail party situations. I just looked at him and he looked at me, and there was this connection. Right away.”

The two talked for half an hour, he says. “We both kinda said, ‘Well, maybe we’ll get to do something sometime together.’ And we laughed, because we were saying the same thing, same time.”

When Ali, Mortensen and Farrelly began emailing during prep for “Green Book,” Ali remembered that conversation: “Well, here we are,” he wrote.

For producer Jim Burke, the dream was seeing his friend Farrelly, famous for comedies, pursue a dramatic story Burke always knew he had in him.

“I know that he has a tender heart,” Burke says of Farrelly. “And I do believe that in this story, which could have some sharp edges on it with both of these characters, that he would handle it tenderly.”

Burke admires Farrelly’s overall approach. “He’s both collaborative and has a point of view,” he says. “And they don’t interfere with each other. He knows what he wants to do, but he’s open to other ideas.”

Farrelly’s democratic approach also appealed to Ali. “Peter is by far the most collaborative, open director I’ve ever worked with,” the actor says. “I can honestly say that from the first day I met with him, Peter has said, ‘Hey, if you’ve got ideas, if you think something should be different, let’s talk about it.’

“Because, as a director, he clearly openly, unapologetically approaches directing as a student.”