I applied mine while the manifolds were mounted on the motor. The foam brush has a tapered straight edge that makes applying it along seams easy. If there are scales of rust then I would remove and clean them first. It goes on watery and you can apply as many coats as needed. Unlike paint, which can bridge texture, graphite will not because it flows into the metals pores. It will look dark at first due to being wet but after a couple of engine cycles it will lighten just a little.
