They are suppose to be coming out with a 2013 taillight style for the 2010-12 body. I think Raxiom is suppose to be making them. You can't just make the 2013 taillights fit since the bottom of the tail light is straighter than those in the 2010-12's.
I talked to Matt at American Muscle last week. He told me the prototype folks are working on them now and they believe they'll be released around the holidays.
I'll take a small gap that only another mustang owner would notice any day. Unless FORD makes a similar taillight to fit my bumper in the future, I would rather have the part that has FoMoCo stamped on it. Not building a show car here. Just wanted to try them out to see if they would work.