I dont know what your budget is, but have you seen the OTA pipes On3 is selling? $250 shipped... worth a look.
http://www.on3performance.com/shop/on-3-performance-2011-2014-mustang-over-the-axle-pipe-set-304ss/
You would either need to trim the valance or go for a 13/14 rear end swap. Bumper, valance and tail lights. I don't think the 13/14 valance fits on the 10-12 Gt500s
You might want to post this in the 2011+ mustang GT and V6 section also, a lot of those guys like using these mufflers on those cars and $200 is cheap for them.
I have a set of OEM 2014 gt500 quad tip mufflers if you are interested. I know you said you had a 2010 so it would require modifications, but I figured I'd ask
I have some Borla s types for sale, looking for $450 + shipping. If you are interested in going quad tip, I also have a set of OEM gt500 mufflers off a 2014 and looking for $325 + shipping. Let me know.