There's a book, "Hepburn's Law" that's available as a PDF online if you search for it.
There's also a number of bits in articles by Charles A Smith discussing Hepburn, since Smith was involved with some of Hepburn's programming when he was competitive.
There's also information on this site discussing a bastardized Hepburn routine, with further discussion by a user name TwiceBorn who describes the A, B, and C routines and some of Hepburn's philosophies later in life. Here's that discussion: http://tnation.T-Nation.com/free_online_forum/sports_body_training_performance_bodybuilding_article/hepburn_solution_for_strength_and_power_1
He was a very impressive lifter, and also seemed to be a fairly introverted and socially awkward guy. Growing up self-conscious with a club foot and vision problems can do that to you. He put a lot of emphasis on the mental component of lifting.
In general, his approach seemed to be about accumulating volume with a weight before increasing that weight, and switching up programming as soon as things started to plateau. Keep the same lifts, just program them a bit differently. He also put focus on developing both the "strength" capacity in the 1-3 rep range, and "size" capacity in the 4-6 rep range. Sometimes in the same workout, sometimes in different workouts, sometimes in alternating training cycles.
One of the more important takeaways was that he focused on long term term results and gradual progressions instead of the more peak and trough approach that many other lifters take.
Somewhat interesting is that for the overhead press, over time he gravitated toward 8 sets of 2-3 reps, which is almost exactly the same as John Davis and Ronald Walker, both of whom were also phenomenal overhead pressers.