I just did this myself recently, and didn't go quite so precise as you are doing here.
My thinking was based on the fact that there are pistons both sides of the disk, which will adjust to the new disk location even if it is even slightly off-centre.
I measured the disks, outer edge to outer edge, on the 919 wheel, then the F3 wheel, found the difference [around 9mm IIRC], halved it [=4.5mm], and used that as my shimming thickness guide. Ended up with a couple of stainless washers at each caliper mount point and called it good. Loctited it all together, 1600km ago.