well the question to you is! did you buy from the manifold back,the cat back,or just running off stock cat & pipes & just adding the muffler?
1.if it is from the manifold back everything should go right together
2.if you got from the cat back you should only need a 2" to 2 1/2" pipe adaptor (adaptor going into the cat or outta the cat!) depends on it if you bought this or not)
3 your going to need 1 or 2 2" to 2 1/2" adaptors.. 1 if you just go from exsiting pipes into the muffler & come out with 2 1/2"
3b. if you try running 2 & keeping all old pipes in & out the muffler your kinda defeating the purpose of what you are tring todo! just get the extra 2-3 feet of new 2 1/2" pipe & run fresh coming out the muffler & to the rear end!
JUST WELD EVERYTHING SO YOU HAVE NO LEAKS.(If you use the clamps then you will still always have some kinda leak)
this is a video of what a member on here did!
http://therangerstation.com/forums/showthread.php?t=56136