Not hard. Got one on my 3.9
I took sawzall and cut the old one out and used 2 muffler clamps to hold the new one on.
I went to parts store and got guy behind counter to lookup an OEM muffler,
Then got him to check the inlet and outlet diameter,
Then got a glass pack with same dimensions. and 2 muffler clamps.
Loud though. Be sure to put the tail pipe all the way out from under the truck or you wont be able to hear yourself think.