Nail it to the bottom of the grille? Drill lots of holes in the black part? Fit an air dam below the grille and fit it to one side? There are options!

At the end of the day the critical thing is to be able to get enough airflow through the radiator core to cool the engine. I've said it before and I'll say it again, ducting from the nose clip to the front of the radiator, especially over the top of the radiator, to force what gets through the grille through the core is really really important. The size of the mesh on the grill matters too, too small and it blocks too much, too big and it won't protect the core from stones. Finally, the way the grill mesh is bent matters, there's an open profile and a closed profile on expamet.
Guy