You can get most of that dent out of the pipe with some creative plugs, water and a freezer. I've removed large dents from pipes before by plugging the stinger, fill it with water, plug the large hole the header connects to without spilling out any of the water, then put it in the freezer and let it freeze. The expanding ice will push the dent out. It may take a few freeze/thaw cycles depending on the dent, but at the very least, it will improve it.