Anything but Straight off a header designed for 2-into-1 times 2 will be detrimental.
We only have ONE bank of Cylinders.
WHY Have Dual Exhaust?
Either run one pipe for each Cylinder, one for each pair of Cylinders, or one pipe for all 4.
Whatever you do, any Splitting after merging will be nothing more than Show, and possibly be detrimental to Horsepower.