When shimming the sector gear you will need to take into account what components it interacts with:
On one side you have the spur gear, on the other side you have the tappet plate and on top you have the piston rack.
Spur gear interaction is easy, shim the sector low enough to have a tiny gap between the upper flat side of the spur and lower flat side of the sector.
Rack is also easy, as most piston racks allow for plenty of movement anyway.
Tappet plate is where it gets tricky.
At first, have the gearbox with just the tappet plate installed, close it and check if the plate moves freely, if not the plate needs slight trimming.
Then open the gearbox, install the shimmed sector gear and close again with the tappet plate.
Tappet plate should be able to still move freely while the sector gear is in there, also try to rotate the sector gear as if it was actually cycling the piston and check for binding.
Should there be rubbing, you will need to lower the sector gear. I recommend using 0.15mm shims along with 0.1/0.2s because you get an extra level of adjustment.