Okay, I got the header installed today!
First, things nobody tells you:
1. The stock manifold gasket is a double-layer stainless steel gasket. You can reuse it.
2. The stock manifold bolts and nuts can be reused at least once. The lower bolts should be fine to reuse as long as they aren't damaged. The upper nuts are copper and probably intended to replaced with each use... but, but you can get away with reusing them at least once.
3. The header doesn't come with any hardware. You'll need some to attach it to the cat-back. I just used the OE spring-bolts, but the stock manifold uses captive nuts. So, you'll need at least some nuts to fit that. Or if you want, you can replace the bolts, too.
4. You WILL need an O2 sensor socket!
Removing the stock manifold took 3x as long as installing the new header. It took me something like 2.5 hours total. Why so long? Two reasons. First, I've never in my life actually "needed" an O2 sensor socket. I've always managed to get by with a 22mm combination wrench. The way the upper O2 sensor shroud is designed, you need a socket... but, I was too stubborn to go buy one. The problem is that you have to remove the manifold heat shield to access the upper manifold nuts. And to remove that shield, you must remove the upper O2 sensor. My solution was to unbolt the shield, that gave me enough room to get a wrench on the right-side upper nut. But, to get to the one on the left, I had to bend the heat shield. And, of course, that nut was one of two that were Really****ingTight. I had to use a cheater pipe on 3 of the 4 manifold bolts to get them loose... two of them were just stupid tight.
I didn't take the time to read the manual, but it appears that no thread locker or antisieze is used on the manifold bolts. And upon reassembly, I just tightened them "good and tight" with a standard box end wrench. I'll recheck them in a week or two.
Weight of the complete manifold/cat assembly with heat shield and everything that wasn't reused with the new header = 9lbs 14.2oz. So, about 9.9 pounds. Compare to the 5.5 pounds of the replacement, that's 4.4 pounds of weight savings. (woohoo!)
As I was installing, I realized that the necking down of the collector pipe to 1.5" OD that I thought was done for anti-reversion was actually done to allow the OE exhaust donut gasket to be reused.
Fitment was good enough, but not perfect. The upper O2 sensor bung is off to the right by a couple degrees, which puts the end of the O2 sensor a half-inch or more to that side. This makes the wiring to that sensor aaaaaalmost too short. There's enough cable there to make it work if you pull the cable out of its bracket. I opted to just bend the bracket a little bit.
The fitment of the collector flange to the cat-back was also off just a little bit. No so much that it wouldn't go together, but not a perfect fit. I'm sure this is why they use the flex pipe.
Overall, for the price, I'm not at all unhappy with it. Once I got the old manifold off, install took maybe 20 minutes. And I was getting tired and slow by then!