Originally Posted by monolithicjoe
for the looks of it, its welded on.
Chances are it's the original exhaust, which was all welded together and assembled on the car as one unit at the factory (before the rear end was hung). Most exhaust shops won't cut off and tamper or remove a cat. However, you may find a local shop that will do it anyway.
The only way to remove it is to cut it off. You can do that with a reciprocating saw if you have access to one, but then you'll need to have it welded back onto the car which leads back to finding a place that will do it since it's gutted (and getting it there with the open exhaust). If GM used a common size for the pipe diameter, you could reattach it with band clamps. However, they used an odd ball size. I'm not aware of anyone making band clamps that will fit the factory pipe.