There is nothing specifically prefabbed for the EXT. I got a JBA Headers single 3" and had to extend it using strap style clamps. Don't know if you could do the same with the Magnaflow dual.
There is nothing made for a 5.3 engined 360, believe me, I've tried. Some here have said that the SS system will work but, Magnaflo and other manufacturers have told me that it will not fit up ...Mike.