The problem I found when I did mine was that part of the sump passes down between the two pipes where you need to cut it, so you can't just take a hacksaw to it from underneath and saw both pipes at the same time. I ended up using a wire pipe cutter and doing each pipe in turn, in-situ, with a jubilee clip either side of the wire as I was cutting. I just took my time pulling the wire back and forth over each pipe in turn. Took me 15-20mins to cleanly cut through each pipe. De-burred it with a file / emery tape then clamped the the Danmoto decat pipe on, refitted the end can and bob's your uncle, job done.
I've since had it remapped by Geoff at Hilltop. It still seemed ok but was running lean. It's running sweet-as now.
The best option would be to drop the headers and cut the pipes off the bike but I fancied having a go myself. Just make sure you cut in the right place so you can run as much of the remaining headers up inside the link pipe. The Danmoto link pipe came with the cutting instructions and I did also use the fitting kit and hanger brackets to hold it all on underneath, although you could probably get away without that.
Good luck with it and let us all know how it goes.