Not one shred of evidence would support that idea. I'm stunned anyone would even ask this question -- it's on the level of asking, "Is the color of our sun blue?"
Ron Howard
You're probably thinking of Peter Coyote.
It depends on the horse but if you were riding a very fit horse and you stopped for lots of breaks then yeah you probably could.
Cremated, Ashes scattered. http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=1730
Yes, however John Wayne was never comfortable around horse, and shot riding scenes as quickly as possible so he could get past them.
Yes, Hentry Fonda served three years as a Quartermaster 3rd in the Navy and as Junior Grade in the Air Combat Intelligence in the Central Pacific. He earned a Presidential Citation and a Bronze Star. He did not want to be in war films but the real war. He had also raised money for the defense of Britain.