The Heartbreakers recorded and toured with Tom Petty for decades, going back to when they were just kids in Gainesville, Fla. Over the years, they've taken on many roles with Petty's music: performers, songwriters, producers. Now they're adding another: evangelists.

Since Petty's death last year from an accidental overdose of prescription painkillers, Heartbreakers Benmont Tench and Mike Campbell have been working with Petty's widow, Dana, his daughter, Adria, and recording engineer Ryan Ulyate to put together the upcoming four-disc box set An American Treasure

The collection includes original recordings of some of Petty and the Heartbreakers' biggest hits, as well as demos, outtakes and live performances from throughout their career, including their earliest incarnation as Mudcrutch. The box also features 10 previously unreleased tracks.

Petty's bandmates hope the set gives fans a rounded view of their late leader's work and talent in a new interview with the Los Angeles Times.

“If you listen to the lyrics all the way through, it’s seamless," keyboardist Benmont Tench said of a previously unreleased 1993 track called "Lonesome Dave," which is included on An American Treasure. Inspired by Dave Peverett — or at least by a desire not to follow in the late Foghat singer's footsteps — Petty wrote the lyrics to the song on the fly while the band worked out the music. "That’s the kind of writer he was. … I always say I’m an evangelist for Tom, because I think the world needs to know just how great he was.”

When another previously unreleased track, "Lost In Your Eyes," was uncovered, Campbell was surprised to hear the maturity of the recording and the soul in Petty's voice. “Tom is a rock 'n' roll singer, but this song is Otis Redding," the guitarist told Variety. "He was a soul singer too. When he hits that high note — pure soul.”

Tench recalled another track, a Southern Accents outtake called "Walkin' From the Fire," which was part of an entirely different set of songs created for that album. “It was a crazy record and a crazy time,” he noted. “There was a whole other record that fit the Southern Accents motif, and for some reason we got distracted and started putting on all this other stuff, which was really interesting. But this to me feels like some guy in the South who’s kind of hard, a good person who’s kind of pushed."

Tench said he admired how Petty kept trying to use the lyric "Don't put me in a corner" until he finally made it work in "My Life/Your World." “I liked the way Tom would take [abandoned] lyrics and go, 'No, I’m not gong to let go of that,'" he said.

As serious as Petty was about his music, his bandmates remembered his humor. “I listened to the words" to "Walkin' From the Fire," recalled Campbell, "and I said to Tom, ‘Don’t you think he’d be running from the fire?’ And he just looked at me and said, ‘Shut up.’”

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