If you have stock duals, and want a direct bolt in magnaflow, you need the mufflex kit(not sure of the part numbers, someone else can help you out). If you just want the magnaflow muffler itself it is not a direct fit, you'll either need someone to weld it in and bend a couple pieces of pipe, or if you can do that stuff yourself then do that.
See this thread for part numbers:
Stock exhaust is 3" single inlet, 2.25" dual outlets. You can get a 2.5" dual outlet muffler and the shop can reduce it to 2.25".