Actor Hoke Howell, who originated the role of Dud Wash, wasn't cast in this episode because this was the year CBS launched "Gilligan's Island" (1964) and they wanted to promote the new show by casting Bob Denver.
This episode stars actors who later portrayed the iconic TV characters Matlock, Mr. Furley, Uncle Jesse, Gilligan and Richie Cunningham.
Although not set in stone, most horses are trained to be mounted on the left side. It's quite uncommon to see Barney mount the horse from the right. There are many trains of thought on the subject of horse mounting, but more often than not, you mount from the left.