Joe talked about Mr. Hogan a lot. He said that Mr. Hogan told him he worked on his left arm for two years. In his video Joe says Hogan worked on the upper left arm and shoulder muscles to keep his left arm straight. The left shoulder moves down vertically as the left arm moves horizontally back following the lead of the right arm around the waist.
Mr. Hogan worked on the extensor muscles from the left shoulder to the arm. The picture shown here is a swing different than what Mr. Hogan describes in his book.
It's classic Norwood. His arms and waist are at the same 45 degree angle at the top of his backswing.