Does anybody know exactly what Mercedes does to their AMG models when they are produced regarding enhancements to the body? Are they using a standard body that they put all the good stuff into, or do they make separate bodies for the AMG models?
Is it possible to find documentation about how they are produced?

On the same exact assembly line as the other models with the same body. Only difference is the sequence of parts that come to the line - all the different goodies are specific to that model, but it's just like any other automotive assembly.