biggest restriction on almost every single 4.6 equipped car is the mid pipe (be it a y pipe or an h pipe). rule to passing emissions is to 1 have a set of catalytic convertors placed int eh stock locations. even the slightest movement of them on that mid pipe and cali smog testers will flake out (unless ur introducing them to ur best friend ben franklin usually). if ur going to go with true duals i say go for it, use that true x piece u were talking about but slap some mufflers on where the tips go. just make sure with the pipes leading to the x you put some carsound catalytic convertors (made by magnaflow) in the factory locations and u should be set.