If you do go with tailpipes and they don't eliminate enough of the drone by themselves, then any cheap bullets (we used to call them glasspacks) in the tailpipes work good as resonators and usually deal with the remaining drone quite well. Do you have room for all that?
You should try to re-position your engine as suggested above. But it looks like you are probably going to need to hammer on your headers. That won't hurt your performance, but will take a toll on the coating.
A piece of insulation there will help to cover up the dent and the accompanying coating damage as well as keep a bit of heat off the box.
