Heh. I will never make a AC-saving manifold ever again. It's such a pain to get the runners so close to the flange itself so it fits behind the AC bracket, and then once it does fit and the person has to install it on their car, I get complaints about how it's too close to the head and you have go buy a special wrench to get to the exhaust studs to tighten it down.
Since 99+ DOHC is 9-bolt, you can't simply use a 91-92 5-bolt header. I say 91-92 header because they are the one years where everything was steel and it's completely weldable. the 93+ manifolds are cast and you just simply can't weld to cast and expect it to go through the heat abuse and weight abuse of 2 different metals and expect it to hold. Sure, Twistec did it, but how reliable was it? It's bad enough that I weld steel to cast when welding differentials, but they usually come out real clean looking, and since there isn't any stress on the pin, I'm not worried about the weld breaking.
