Leave the catalytic converters on, and put the muffler after them. Same place where the muffler is on your truck now.
Or just take it to a muffler shop and give the muffler to them. They'll put it where it needs to go. That sounds like the best option for you.
Your options are pretty broad. Try looking on YouTube. I already posted one video for you. Flowmaster 10, flowmaster 40, magnaflow, Spintech, whatever.