One of the best ways to find out more about Howard Hill is to read his book, Hunting the Hard Way. It describes his methods as well as some of his hunts. It is quite readable. His wife was an English teacher, and I suspect helped him edit it.
Howard could do some remarkable things with the bow. With his accuracy, I'm sure he could easily double the average good shot's effective range on game. The ethics of the time being what they were, I would imagine he took his share of long shots, and managed to connect on more than a few.