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.
If you can read this, thank a Teacher.
If you can read this in English, thank a Vet.
If you can read this in the dark, thank a Coal Miner