There are few resources regarding Content on the Internet, perhaps the best of the lot being here. As it notes, he eased out of illustration into art direction, including a stint at Benton & Bowles, a major advertising agency at the time. This was probably a good career move, given the slow decline in high-paying illustration jobs. As an art director, Content got a steady paycheck and didn't have to worry about altering his painting style to keep up with changing illustration fashions.
Content did good, solid work, but remains somewhat obscure perhaps due to his stylistic similarity to much better-known Cornwell.
A complete set of images for this project can be found here.