I purchased the 3.5 OBX Headers off of a guy on ebay named Sparktech I believe, paid 350 or so shipped new in box, was a good seller, quick to ship and gives you tracking number.
As for the install, I installed on my 02 SE - get yourself PBBLaster and if you have access to heat (torch) get ready to use it. I live in the Northeast, rust is a big issue up here and I stripped/broke roughly 10 bolts off my headers/heatshields/exhaust. Other then that its generally self explainitory if you have automotive knowledge.
Just some food for thought, I had read a writeup on obx headers installed on a 3.5 03 and the dumbass cut the motormount, you do not have to. The motormount I speak of is the rear (firewall side) center crossmember mount, not sure how its setup on the 3.0's but theres a slight clearance issue w/ the downpipe from there, don't stress it when you get to this part - take the time to work around it, never cut/notch a motor mount becuase you loose structual integrity.
Also, the gaskets they give you are ****...absolutly horrible. Head down to Napa and get some stock ones, they'll work just fine and are much better quality. As for o2 sensors, I highly suggest that you use all 4 (in the 3.5 it has 4 total o2 sensors), I was told that if you match the o2 sensors in both Bank 1 and Bank 2 you should be okay to run 2 o2 sims but I am planning on purchasing 4 matching ones to get them all the same and rewire them in, they are 3 wire style. The only struggle I've bene having is soldering the wires, do your best to wire them 100% matching so that way you do not have any intermdiant connections, also make sure you weather-proof them to the best of your ability, shrink wrap and electrical tape do a decent job, but there are other ways.
Just to note, I am not a pro at this I am only giving my advice from the issues I've ran into w/ my install. I have a 2002 SE w/ 110k, the car wasn't very well maintained therefore I had alot of extra work to do. Take the time to do the job right, because I know for a fact I do not want to have to struggle with it again....
Any questions feel free to pm me or email me at
Maltese.Rob@gmail.com Good luck my friend.