Lower valences for both cars are identical, EXCEPT for the size and shape of the two holes where the tips go through. The process.
Remove the real bumper cover (which includes the rear lower valance panel). To get to all the bolts to do this, must remove the tail light assembleys and open both the little "doors" on each side of the trunk compartment. The exhaust tips are attached to the lower valance panel and are not connected to or attached to the tail pipes. You then take the lower valence apart from the bumper panel (no screws or bolts involved). Then unbolt the two V8 tips and bolt the W12 tips (one piece-two tips each) onto the new W12 valance. "Hook" the lower valence to the bumper cover and reassemble. Va La, a W12.