Otis Adelbert Kline mars serie (sword and planet)

The Swordsman of Mars

In “Swordsman of Mars,” Harry Thorne, outcast scion of a wealthy East Coast family, seeks the greatest adventure of his life. He exchanges bodies with his look-alike, Martian Sheb Takkor, and is transported millions of years into the past to a Mars peopled with mighty warriors, beautiful women, and fearsome beasts.
Sheb Takkor, a great swordsman in his own right, must fight his way across the deserts and jungles of ancient Mars to save the lovely Princess Thane and to defeat his arch-enemy Sel Han — or die trying! Edgar Rice Burroughs was the first great writer of planetary adventures.
His one true rival and equal at writing planet stories was Otis Adelbert Kline.

and the sequel :  The Outlaws of Mars