I don't like to use one kit body as reference for correcting another, but Jo-Han's RR body is good enough to use. When you set one next to the AMT body on a flat surface (body only, not assembled kits) the back of the AMT body isn't drooping and doesn't need all that cutting. The lower part of the quarter panel behind the rear wheels does need attention, as does the wheel opening. The difference in the rear window opening (not the quarter windows, but the backlite) might create some illusion of that, but that would be a ton of work to change.
And, when comparing the fender and quarter panel "eyebrows" to photos of 1:1 cars, AMT's could be a bit sharper but Jo-Han's look a bit too long to me.
--Mark