Just because your engine is fresh doesn't mean it's making good compression. It could have any number of problems. Do a compression test on all 8 cylinders and report back the numbers.
Stop talking about spark plug gap or spark plug brand that isn't getting you anything.
That converter isn't doing you any favors, especially combined with the cam.
You're giving up probably 20 ft lbs or more with the exhaust manifolds.
Do get the ignition wired correctly.
Watch this video: it gives a good breakdown of what can easily be achieved with a very mild 360 combo. This engine would have no off the line issues.
Wow, that video has great information, I wish I had watched it before I dropped my 360 in the car. I don't like the manifolds, but they fit and I had them. I will upgrade to headers, most likely a set of Doug's since they look like they fit decent with power steering. The power steering box and having to run the headers through the steering linkage turned me away from the cheaper headers.