Another way to see that the cars arent exactly the same is to look at the rear quarter glass.  They are all different on the cars as well.

Beleive me Gael, we can ALL see why you would think they were all the same car.  Not much really that different about them at all.  Take all the decal off the car, they would pretty much all look the same. 

Good luck, I have wanted to try a custom but I dont know where to start