When I decided to go this route, the first thing I decided to do was research up gorillas. Adult male gorillas a saddle of silver-hair appears on their backs. This hair is really short whilst their arm hair is really long. They reach about 5-6 ft in height, have an arm span of about 7ft 6in and weigh approximately 450-500lbs.(These images were obtained from wikipedia)
Gorillas move around by Knuckle walking where they walk around on all fours with the weight resting on the Intermediate Phalanges. I have a diagram here to explain.
I also decided as part of my research to look up animations. I felt that Disney's Tarzan was my best bet for gorilla animation. Glen Keene's animation of Tarzan in that film was so cool and Young Tarzan will form a good basis for Pocahontas Billams. The Claymation style wanted in the brief I believe is more of a Plasticine feel gotten through the texturing stage, rather than the character design stage. Claymation doesn't mean you have to have the Aardman mouth. These Images come from either Disney's Tarzan Special Collector's Edition book or http://theartofglenkeane.blogspot.com/2006/05/tarzan.html.
I have also got some scans of drawings by Andreas Deja of Lilo, obtained from the book Lilo and Stitch: Collected stories from the film's creators. Lilo has that relaxed feeling required for Pocahontas and she is just the cutest little girl in an animated film.