My thoughts and experiences on grills
I agree with the previous poster that the overlays never seem to fit quite right. I've seen two and they looked kinda bad. I'd also be really hesistant to install one that involves cutting up part of the car. Not because I wouldn't want to cut up my car, but because I'd be worried about the fit/appearance after I cut it up.
E&G Classics (http://www/egclassic.com) has some nice ones, and you can see the pictures already installed. They have both the 'Classic' style as well as a chrome horizontal style one. These are the ones you can buy through the Cadillac dealerships, although you can find 'em on eBay too.
My plan is to hook up the chrome horizontal style one when I get a chance. Unfortunately work is kicking my tail right now!