Need Exhaust Removal Advice

I need some advice about the exhaust setup on my truck. The majority of the piping is stock but at one point a new muffler was welded on. I ordered a TRD exhaust but need some advice as to how to remove the stock system. My issue is rust. See pic.

I think I will be able to remove the O2 sensor ok, just soak it up. But what you guys think about the pipe itself. Those bolts look like they are melted to the Cat. FML.

Anybody have experience with a similar situation. I think I will have to cutt off those cat bolts but don't want to damage the cat. Need advice.

 

Well I can't upload the photos now I'll have to try later. Just imagine a rust bathed cat/exhaust pipe connector (the one with the 2 bolts)

 

lots of penetrating oil.

 

pb buster and an angle grinder with a cutting blade. the o2 sensor is a bitch. i still cant get mine off and am contemplating just getting a new sensor altogether the pipe itself isnt too hard just a clumsy piece to deal with

 

beat that mofo