Got your PM... The pipe is definitely stainless, so welding would be no problem. Are you sure you got the system for the MY05+ models (boxed swingarm, not cast) The exhaust for the cast swingarm ('03-04) will not clear the boxed swingarm. I had a very tight fit on my full system, and had to grind the welds inside the muffler joints to get my mid-pipe to fit properly. You can try mock-fitting the system, leaving all the joints/mounting points loose to see if you can pursuade the pipe to fit correctly. Another solution would be to just remove the catalyst from your stock mid-pipe either by cutting/rewelding or by breaking it up the element (which I imagine would be quite a chore).
original header is the same for all the swingarms, but differs due to the two sump configuration. the termi '03 - '04 header pipe won't fit a later swingarm, as the bend is much closer to the swingarm than the std header. can't really tell just by looking tho.