This book is very similar to the Kung-Fu series with David Carradine. It came out a few years after that. Even the cover bears a resemblance to the Carradine character. Although Slone has long hair and wears a white suite. Mix in a little "Six-Gun Samurai" and you get the basics.
A boy and his dog are playing in the desert by their home when wagons approach. A jolly clown is in the lead wagon. The boy takes him home to his parents. After some niceties, the clown and his crew kill the boy's dad and rape and kill his mom. Burning the homestead down around them. The boy, who you guessed is Slone, escapes the outlaws.
He is raised by a Chinese family who found him half dead in the hot desert. The father teaches him Kung-Fu. After eight years and growing to manhood, Slone sets out on his vengeance trail.
A really short book. 156 pages of crammed in plot action and martial arts. It's a whirlwind that never lets up. Where most books like this space out the hero's vengeance to four or five or more books, this takes care of it in book one. Really a nice surprise read.