I have built a few engines as well and this is my first Porsche. I think this is a pretty simple engine design.
If the machine shop asked me the question of do I machine both surfaces? I would say thank you and go somewhere else.
Here is a 3.2 and a 3.0 flywheel. Even though the 3.2 has a grove or channel between the pressure plat and disc surfaces they are on the same plane or levels so doing one without the other seams difficult.
I stick with the KISS principle and have pretty good results.
