As to whether they work or not, with a good, "complete" system (tubular headers and a low restriction 3 in. system) you should easily pick up ~30-40 hp. I know it took about .4 seconds off my ET at the drags, and also improved the fuel economy. It is one of the two best mods. I've done to mine, the other being changing and advancing the cam.
Most on the dyno get a bit over 20-25 hp on the 6.1 with long tube headers as have the better manifold to start with. The 5.7 manifold is much worse and see a similar gain just using the 6.1 manifold! 25-30 when going to long tube headers from the few dyno charts I could find.
I saw a company... Maybe they were in one of the Dakota's that fabricated headers. They send you their proprietary header kit full of bends, joints, etc.... You fit them together on your rig and then send back the form and they will fabricate you a set. I don't know the name of the company, since I'm sure is will cost over a 1000 dollars... And you can get a used set of srt8 manifolds for 300.
As for the long tube headers... They are all for the srt8... And notching a header that costs upwards of a grand is a tough call. American racing will make a custom set with our square shape ports... But who has 2 grand laying around.