JPC/CPR single both have show to perform extremely well.
I bought the Hellion TT kit about 2 years ago. Install was pretty easy - we did it on jack stands and swapped the k-member at the same time. It does come with its own headers, but as you mentioned, they are basically just reversed, with a Y pipe going to the waste gate. The hellion kit has three mani modifications for fitment. None were groundbreaking. PCM is moved to their provided backet, fuse box gets moved to the side a little, and a new power cable is provided for the Fuse Box > battery because of the move.
Either way, I am sure the bigger singles were going to be more efficient, but the top power wasnt really a goal. I can still break 1000rwhp on 19lbs boost, keep the 6r80, and drive to and from work just fine. The look of the twins up top is really why I settled on the Hellion kit.