I fitted a 4x4 mongoose exhaust to my 3 dr and it catches the bottom of the gearbox . If you look at them closley you will notice that the 2wd exhaust keeps to the right hand side of the gearbox as the 4x4 goes to the left hand side of the gearbox .
All i did to stop it hitting the gearbox was take a big hammer to it and flattened it about half an inch at the gearbox . Problem solved .