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.