It should tell you in the instructions what the different parts you can use to make it stock or make it custom.
Most of those kits were either a 2n1 or 3n1 kit, with extra parts to make it a couple of different ways.
Some of it is just simply different tires and wheels, maybe a different intake on the engine, to the other extreme where they added different body panels to change the look of the vehicle, or maybe different exhaust layout.
You would get others that would be a 3n1 so you could built it Stock, Strip or Street versions.
Whatever the differences, it should be all laid out in the instructions for you.