Pull the rivets (one at a time of course) and re-rivet them nice and tight again, then give the whole muffler body a quick sanding down and then paint it flat black with BBQ paint...
You could tape up the header pipe too, to match it in color and make it look ‘finished’ again.
Of course, if you like and want chrome, my suggestion isn’t going to appeal to you very much
EDIT:
If you did strap on a staight pipe, you could try to fill it with a
baffle and/or
internal mufflerfiller yourself to make some back pressure for tuning and maybe just quiet enough that not every cop for 2 miles around you can hear it...