I've got the identification pages for all of the newer Imprezas, Legacies, and Foresters. It gives a definitve answer to what each item means in the VIN and the model code. The codes seem to be model line specific as some overlap with different meanings...
ie: Model code for the 1993-2001 Impreza has the following meanings:
G : Series : Impreza
C : Body Style : C: Sedan, F: Station Wagon/Outback Sport, M: Coupe
C : Engine displacement, Drive system, Suspension system : C: 2.2L AWD, E: 2.5L AWD
I'l update the entire list with the information at a late date. It's bedtime right now.