I have the Walker BTM (Big Truck Muffler) on my 05 X.
You'll need to cut the hangers off the old muffler and weld them onto the BTM in approximately the same places. The hanger ends that attach to the truck are not moved.
Just clamping the pipes onto the muffler will probably be adequate, but any decent muffler man is going to clamp it together then weld it up tight. Since you must have a welding machine handy anyway - to weld the hangers from the old muffler onto the new muffler - it's not much more work to go ahead and use the same welding machine to finish the job.
You'll need two 3.5" muffler clamps. Not available at most auto parts stores. Not available at most muffler shops that specializes in cars and light pickups. Order online or you may have to go to a truck parts store to get them.
The trick to the install is to remove the "S" pipe in front of the muffler and turn it over - 180 degrees. The result is a straight shot from the exhaust pipe to the tail pipe - and the BTM needs a straight shot.
The BTM is several inches longer than the stock muffler. So part of the install is to remove the right amount of exhaust pipe from the S pipe. Measure carefully.