I just did the reverse install of the V&H 2:1 Comp on my '08 NRS. Gaskets are a MUST. They were less than $20 I think. I also swapped exhaust on my Softail, and purchased those gaskets at the same time. They appear to be a bound, tightly-woven steel and some other "mystery" binder. When you remove the existing exhaust, you'll see that it has been crushed into the shape that fit your old pipe's rolled edge. A slight variance in the shape and placement of your replacement pipes will allow for leakage. And be careful tightening the nuts that hold the flanges on. I've heard of more than one person breaking the stud. THAT could turn into a royal pain. Especially on the rear.
I retained my O2 sensors in my swap, but I'm guessing that if you're running without now, you can probably run without them. But with the V&H setup, you should have an additoinal tuning device in the mix. I've got the SERT, V&H make their own. When you swap the exhaust, it definitely won't run the same. You'll need to get a dyno-tune. I'm considering going with a Zipper's Thunder Max Autotuner, but can't advise one way or the other as to how that will perform in your situation. Cobra makes one that ditches the O2 sensors, and uses a sensor on the crank.
Good luck with your swap. You CAN get the quiet baffle for the V&H setup. But it's not really that quiet.