Yeah, you got it..the cats after the headers and the blob resonates:)
you can use the cat as long as there are no holes in it, cracks in the pipe, or rattling sounds from inside it. put it back on and fab a system from there back. you could cut off the flared end and use it again on your new system. you can cut the hangers off and reweld them to the new pipe. then run your system for a while until the cat does go, and replace it when you need to.
Geoff