FLY AWAY HOME: Memoirs of a Hollywood Stunt Man by John Weld (Mission Publishing: $19.95; 249 pp.). It's a mystery why John Weld would identify himself in this autobiography as primarily a film stunt man. So he was--in the early 1920s, doubling for Stan Laurel, Tom Mix and Zasu Pitts, among others--but he has led an assortment of seemingly incompatible lives. As a newspaperman in Paris in the early 1930s, Weld befriended the likes of Legs Diamond, James Joyce and Alexander Calder; a few years later he was back in California writing books for Scribner editor Maxwell Perkins. The following decades found Weld all but drowning in a freighter accident while starting yet another successful career as a documentary film maker. Weld says he's left out many incidents in his life, and embellished a few facts, but it's hard to imagine that the author, now 86, had to exaggerate very often. When you've fenced a French nobleman to a draw over an affair with a countess, then told your opponent that you learned the art from John Barrymore in Hollywood, and had the incident duly recorded in the New York Herald Tribune . . . well, who needs to make stuff up?