"Now, Elvis, he was just...uh... gone!" says Tom Petty, bouncing on the balls of his feet a couple of hours after a triumphant two-encore set at San Francisco's Winterland Ballroom. A funny faraway gleam glazes his eyes.

"Did you ever see him do 'Reddy Teddy' on the Sullivan show?" he wonders. "Now, man, that was real gone. His hips were swivelling and his eyes were wild and cross-eyed. He just kept banging on his guitar, really wailing, and he shuffled 'cross the stage like he was on wheels. Never seen nothing like it before."

If Tom Petty had a time machine in his backyard—say the cobalt galactic wonder that transported H.G. Wells into the land of Eloi and Morlocks—he would set the dials for downtown Memphis, circa 1955, at Sun Studios where Elvis was cranking up his chromosomes for a first take of Kokomo Arnold's "Milk Cow Boogie Blues."