If I say buy a magnaflow muffler and unclamp the old ont which is about a foot and a half away from the coverter could i cut of the end that is welded to the old muffler and clamp that on to the otherside of the new muffler or do i need to get an all new pipe run from the new muffler?

 

The factory muffler is longer, has a different offset, and includes a hanger on it. So, the new muffler will need additional pipe, a few new bends, and a hanger added. To do it correctly is usually easier at a muffler shop. If you have the same ID muffler and the same OD pipe, you can cram and clamp. The placement, heat shields, and hanger location will be off. I'm assuming that we're talking late model F-150s.