JP,
First of all, Welcome to DodgeTalk! You have come to the right place to learn about what people are doing to their rides!
Does that truck have the MDS setup? If it does, you may want to do some research on that Flowmaster before you buy it. Seems that when MDS activates, it produces a VERY unpleasant tone from what many of us have been reading.
As for your question, Im not sure the exact length of pipe you will need, but any exhaust shop will be able to install and fab that for you for little to no $$$
Good Luck!