Well, after pulling my hair out for a month trying to figure out why the car won't start, I finally solved the problem yesterday. See this thread for the symptoms. As it turns out, I missed one ground, which was causing all sorts of problems. I finally managed to track it down yesterday, and voila, the car fires right up. And it is LOUD (no exhaust after the Kooks headers, at the moment)!
By the way, that is a 4.6L DOHC in a 90 XR7. Now I just need to finish up the interior (it's from a 97 LX), install some exhaust, and have it dynotuned. Then it's time to hit the pavement.