Recommendation for Headers/Exhaust on 416

You won't see a bonus from 3" pipe until you are close to 500hp. With the cam choice and heads, I don't see you getting near it. Closer to 400 with big torque, but it will be done at 5Krpm. The smaller tubes are fine, and you dont need 3". You will not feel a difference between the two sizes. I would get a simple custom bent 2.5" comrpession bent system. That will keep you for a while, even as you do upgrades.