I just did the install on the 2011CS/GT500 rear facia onto a 2010 Roush 540RH. It took 3 of us approxiamatly 2 hours total and we were not trying to set a land speed record (I had 2 buddies there to hold the bumper after removal so I didnt have to remove all the light connectors, otherwise you can do this solo). Tools required a very short phillips screwdriver, and I mean very short unless you want to remove your rear tires. You will also need a short flat tip screwdriver to remover the plastic pop fasteners that hold on the lower facia. You will have to remove the entire back bumper to reach a 4 screws however the bumper comes off the car like legos once you take the screws from the rear fenderwell.
I ordered the part through a Ford dealership, and trust me you can do this install yourself. If you have any questions shoot me a PM or we can hash it out in this thread. Enjoy.
Jimmy