Inside Boyd Holbrook's Johnny Cash Transformation for A Complete Unknown: He 'Made It His Own' (Exclusive) 

Boyd Holbrook is detailing everything that went into his Johnny Cash transformation for A Complete Unknown.

PEOPLE has an exclusive behind-the-scenes video, in which Holbrook, 43, along with his costar Timothée Chalamet and director James Mangold, discusses his performance as late country star Cash opposite Chalamet as Bob Dylan.

Holbrook says in the clip that he "did a voice coach, singing coach, about two hours a day for five months, just immersing myself in him, his voice."

The star's iteration of Cash intersects with Chalamet's Dylan multiple times in A Complete Unknown. Director Mangold, 61, previously worked with Joaquin Phoenix to bring Cash to the screen in 2005's Walk the Line. Mangold says in the clip that he "just felt Boyd would have fun with this" when he cast the part again for the Dylan-centric biopic.

"Boyd made it his own. It feels just as authentic and true as Joaquin Phoenix's performance as Johnny Cash," Chalamet, 29, says in the video.

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer​​, from celebrity news to compelling human interest stories.

Mangold adds that he was interested in how Holbrook's "masculine, dark energy inhabiting this role" would play opposite Chalamet as Dylan in the earlier years of Dylan's career.

Holbrook describes learning to portray Cash, who died at 71 in 2003, involved "carving out sort of this hollow tree within myself to get that resonance, which was a process, man."

"It took me a long time to do that. Dyed my hair brown, put on some more weight, put on a [fake nose], and we even had spacers behind the ears. But playing make-believe at this level is pretty high," he said.

A Complete Unknown received eight nominations at the upcoming 97th Academy Awards. Chalamet is nominated for Best Actor, while costars Monica Barbaro and Edward Norton are nominated for their performances as Joan Baez and Pete Seeger, respectively. Mangold is nominated in the Best Director and Best Adapted Screenplay categories.

"We pay money to go see a movie because we want to learn something about ourselves or the world or feel something, and that's gonna only come from finding the part of that person that is also in you but always carrying the part that is you with it," Mangold says in the video.

A Complete Unknown is now available on digital.