From Thomas Mallon, author of Mrs. Paine's Garage, a disquisition on the JBS, plus a small review of the JBS-unaffiliated biography John Birch: A Life, a level-headed book that I happen to be reading now and can recommend to those curious about the life behind the legend. The JFK assassination is discussed, interestingly, in Mallon's article:
http://www.newyorker.com/magazine/2016/01/11/a-view-from-the-fringe