Exhaust installation questions

Hello all, I received my new Eberspaecher exhaust last Thursday, and today I started hacking out the old stuff. The cat to resonator bolts are thoroughly rusted into the collar on the cat. I've chipped away all the
loose rust and heated the collar to dull red heat with an acetylene-air torch. The preload springs were not enough to budge it, so I have whooped on it with a big hammer. They are holding tough. Any suggestions would be greatly appreciated.
On another note, Should the muffler clamps be installed in contact with the muffler itself, or would it help to put a strip of fiberglass cloth between the straps and the muffler? The can always seems to rust where it contacts the straps. It's also possible that the glass cloth would make it worse by holding salt water.

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