“Gunsmoke” star James Arness is hitting the trail again — only this time it’s to a bookstore near you. For the past 18 months, Arness (who, as the CBS western’s Marshal Matt Dillon from 1955-75, still holds the record for starring on the longest-running prime-time series in TV history), has been working on “James Arness: An Autobiography,” to be published this fall by McFarland Books. The book, Arness tells PEOPLE.com, covers his childhood, his WWII experiences (Arness received the Purple Heart), his family (he and wife Janet have been married 22 years) and his career, which besides “Gunsmoke,” included his being under contract to John Wayne’s production company for three years. (Ironically, it was Wayne who was first offered the role of Dillon when the radio series was about to hit TV.) “Working with John Wayne, you became a part of his family,” Arness, now 77, recalls. “It was like being with Robin Hood and his Merry Men.” Since his last outing in Dillon’s boots (1994’s “Gunsmoke: One Man’s Justice”), Arness, who owned two private planes, was very much into flying, but had to give it up in 1999 when he found himself not spending enough practice time in the air. Those hours, he says, are now devoted to, among other things, his work with United Cerebral Palsy and seeing his younger (by two years) brother, A&E “Biography” host Peter Graves.