Opening up 318 ports to 360 size

I don't think you'll see a lot of benefit because the runners are sized at 318 port dimensions in the plenum, too. Is it the EGR intake or a type Z with the crossover port between #4 & #7? I think you would see more of a benefit by shortening the runner dividers back from the plenum, but I would leave it alone until you get your manifold of choice.