The only two pieces (besides the mufflers themselves) that you need are:
Rear trim panel (51128052677) to accommodate the quad exhaust
https://www.ecstuning.com/b-genuine-...r/51128052677/
Rear diffuser bumper lip (6431223248810)
Something like
https://www.ebay.com/itm/Rear-Diffus...5/253195041707
You can also get these two pieces in one piece, but the fitment is apparently questionable. Something like
https://www.ebmotor.com/product/rear...-2012up-b203f/
https://carbonfiberhoods.com/2011-20...ce-429958.html