Model Sheets are guides for artists so that every time they draw a character the character always looks the same or "on model". Usually they are a series of turn arounds, profile images of the character in question. Some also include emotional and characterization guides with them (facial expressions, body language, etc.).  One of the best collections of model sheets in a book related to film I've seen was in Disney's Aladdin: The making of an animated film. They showed the wide gamut of model sheets used for the characters, including color guides and silhouette.  

Anyway, in the case of Benjamin J. Grimm here, you may have to make due with referencing paneled comics. Not the best choice but as I said, I'm not sure that guide book exists anymore outside of conventions.