To do traditional duel cooling, you need to have an exhaust manifold tapped for 2 lines and a head tapped for 2 lines. Manifolds designed for dual cooling (such as the westcoast) have a place for dual cooling. The westcoast for example has 3 flat spots, 1 in the middle on 2 on each sides. Put a brass threaded plug in the middle and a 90* fitting on each side. If it's only cooling from one side, just tap the other side.
The head has a flat spot to tap. It looks just like the place that's already tapped. Tap it in the spot that looks just like the other spot. There is a chance you have a head that doesn't have this flat spot. It could be tapped anywhere I guess. Usually the tap is placed on the same side (left or right) as the other fitting, and in the same location on the side opposite (So if the fitting is front right, you put the other fitting back right, symmetrically.)