From your photos, I note that your muffler is attached with bolts!
Good luck on those bolts when you try to replace that muffler.
Just broke two off when trying to replace the muffler on my Ford 1920.
Drilling with left hand drill bits works, but is not an easy fix.
If you can get those bolts out now (without breaking them off) you should consider replacing them with studs.
You can always use a nut splitter if the nuts then become frozen to the studs.