I can provide some insight, just replaced the headers on my V6 with Spec-U headers from URD. It's pretty straightforward but I have a couple of tips for stud removal:
1) Use a good penetrating oil on the studs the night before (I like Kroil)
2) Heat the studs up red-hot with a torch before trying to break them free (maybe hit them once more with some penetrating oil as they cool)
3) Despite doing the above, I still snapped two studs while trying to remove them. I was able to get one off using the ol double nut trick, but one wouldn't budge
4) After swearing and bleeding for an entire evening I used a pair of channelock pliers and it was able to turn the mangled stud out easily!
The rest of the job is very straightforward... I had to disconnect the steering shaft to fit the driver's side manifold but that's because the Spec-U headers are funky shaped. I do recommend starting on the passenger's side because it's easier, much more room without the starter and steering shaft in the way. I'm on my phone right now, otherwise I might elaborate a bit more but the studs were really the only difficult part. Good luck!
