The Swordsman of Mars (Otis Adelbert Kline's Mars)

Harry Thorne had lost everything: his business, the love of his life, even his own self respect. As he's contemplating suicide he's made an incredible offer. He can go back in time and switch places with a look alike who lived on Mars millions of years ago when it was a lush, beautiful planet full of promise and adventure. Seizes his last chance at salvaging his life is transported millions of years into the past to a Mars peopled with beautiful women, mighty warriors, fearsome beasts, and awesome magics.