Actually did something audio related with the car today, it's been a while!
I found out that the OEM speaker "grille" in the doorcard (the perforations) measured pretty much exactly 165mm, the same as the outer diameter on the midbass drivers that are going in the doors. It also had a small ring on the outside of the perforations that can be a base for a new trim ring/grille.
So I ordered a 165mm hole saw and promptly cut away the perforated part.
As you can see, the OEM speaker (and cutout) was not centered in relation to the grille, so I will have to cut a bit of metal and center the new speaker rings in relation to the door card.
From earlier I had some pvc speaker rings made to the cut out and outer dimensions of the Focal 6WM drivers. Now they fit snugly in the hole I cut:
I taped three of them together to reach the door skin so I could see exactly where they need to be mounted to center with the door card.
I marked out where the door skin have to be cut, and will make some test spacers that are a bit shallower than the 3x rings I tested with. I think I want to have the face of the speaker just inside of the door card and make a new, more open grille. Probably with some hexagon metal mesh.
Good to have something done after a looong time with no activity.. Even if it's such a small task like this.