The subject of the "real" Captain America motorcycle is a prickly one that I touch upon in the book Legendary Motorcycles, which mentions the fact that two alleged Captain America bikes are endorsed as authentic by Dan Haggerty (aka, TV's "Grizzly Adams"who handled the bike during the film's production: one, owned by J&P Cycle's John Parham (seen in this photograph), and the other-- which was lost in the fire-- owned by Gordon Granger.
However murky the authenticity of the burnt bike may be, the legend of Captain America is far bigger than one modified Harley-Davidson, whether or not it appeared in "Easy Rider."