Is the part that's supposed to be black lower than the chrome edges like it appears to be on the real car? If it is, you could start by painting the entire trim piece black (which you would have to do if using Alclad anyway), then carefully run a bead of liquid mask into the low area in the center. Then lay down the chrome Alclad. You need to do at least 3 layers of the liquid mask (let dry about 15 minutes between layers) in order to be able to easily peel the liquid mask after the chrome on top is cured. Use a toothpick to start the mask edge peeling, then grab with tweezers and carefully peel it off. As long as your chrome coat is nice and thin, you won't have to worry about little chunks of the edge of the chrome accidentally coming off with the dried masking fluid. If the black area is higher, it can still be done the same way, it'll just be more difficult to get a nice, straight edge.