UPDATE: Harley-Davidson historian Bill Rodencal told me this is Gerald "Jerry" McGovern. Upon further research, I found that McGovern is shown here after the 1957 Jack Pine Win (he also won in 1950). The race is run over all types of terrain, trails, tall grass, hills, water crossing, with various opportunities to earn (and lose) points. It's on a points system. In this very race, in 1957, were racers like John Penton . . . so us Harley enthusiasts can proclaim proudly that John Penton was beaten by a guy on a '57 Sportster ! Hip Hip Horray for Jerry McGovern of Grand Rapids, Michigan.
(PS: It looks like he made little extensions to raise the front fender....)