You have to be kidding me...

[Digital]

The direction the ports faced has nothing to do with whether you can invade, only requirement is a linkage of fleet, without enemy fleets in the same sea in the linkages. You also need a port to invade from a province to another province seperated by sea. The province you invade does not need to have a port. For example, if you are invading Ireland from Wessex, Wessex needs a port while Ireland needs none.