For anyone that is still curious, no one would touch the existing chimney. I'm going to move the stove to the corner of the room and do a through-the-wall installation. Will run 15' of Duratech chimney pipe.
Thanks for the update patdale. Sorry there wasn't a good fix for the old system, but I'm glad you are going to get things set up correctly. Can you reuse the class A pipe and connector, reconfigured with a new tee and thimble?