Do you have to take off the valve cover to replace the exhaust manifold?

I've done this. No. Remove the air breather assembly to gain access to exhaust manifold. Disconnect O2 sensor that runs through heat shield. Remove heat shield by removing 5 nuts. Disconnect catalytic converter from manifold by removing five nuts. Remove the head to manifold nuts. Remove manifold. With the right tools and a bit of luck 1 hour.