Like all things Porsche, it's complicated, and has to do with the presence or absence of a vacuum capsule, the location of the vacuum port the capsule is connected to, and the objective of the control system.
Early cars - no vacuum capsule, could rotate either way. Bosch was using clockwise, so that is what Porsche used.
Later cars had vacuum capsules with several objectives, but the key thing to remember is that vacuum canisters can only pull the distributor plate when vacuum is applied. If you want that to produce spark advance, you need the distributor to rotate one direction, if you want it to retard, it needs to rotate the other direction.
They did away with the clips because it did not hold the cap tight enough. There is enough play to rotate the cap several degrees. The "push and turn" eliminates that to a large extent. The screw style terminals allow wires that produce a more consistent grip on the distributor terminal.
