The manifold is physically attached to the engine block. What you are speaking of sounds like the mid pipe or y pipe, which connects to the exhaust manifold to the cats.The can you see on this pipe is probably the cat and the sensor is the O2 sensor. You should just be able to order that pipe or have one custom built. I would use the damage as an excuse to upgrade the complete exhaust system

. As for the brand of muffler, I am sure some other V6ers will chime in with suggestions.