Monte Carlos had 12" brakes.
You can use the Monte Carlo brackets with your factory calipers to install 12" rotors.
If you want to upgrade to F-body standards you will need brackets and calipers from an f-body with the appropriate pads. With those parts, and a tiny bit of fabrication you can buy the 12" rotors that are made to fit the Monte Carlo, or aftermarket rotors that fit your application and have dual piston aluminum calipers that are superior to the GP calipers.