All four mounted now...
I took the car up to ~110 km/h and double-checked them. All looks good.
Started on the grille blocks as well. I just used some scraps of wood to sandwich the factory grille, and screwed coroplast into the scraps:
Before...
Now:
Upper is now completely blocked. I'm going to reposition the plate to the lower right grille area, leaving a center opening about the size of the plate itself.