I'm pretty sure they're welded. But once you go that deep you're committed at that point to tear something up. If you are successful and are able to jerk the guts from the muffler cases, the tone the empty cases will make your neighbors, dogs, cats, small children hate you, and most likely Mr. Popo too.
These folks appear to make a muffler / turnout in stainless.
https://www.hotrodhotline.com/pr/201...es_side_pipes/
Or Firefly. Pricey for what you get though.
https://fireflyperformance.com/pipekit/index.htm