I was told I needed lower grilles in place to install billet grilles, I was missing my passenger side grille. (Or do you say grill?) Anyway, I looked at mounting it without the factory grille, and it wasn't easy, but not that hard, but both sides weren't the same. Even with the original grilles the toggle bolts they put with the kit wouldn't have worked, the bolts weren't long enough to let the toggle flip up after going through the original grille, and getting rid of the original grille would help airflow.
On the passenger side there's a metal rod on the outside that I used to put a tie wrap around, and I had to make a sheet metal bracket to hold the grille on the inside. On the driver's side there was no metal rod so I used a block off plate to hold the outside part of the grille. I used some scrap sheet metal to make all 3 pieces, the inside pieces were similar. I cut the driver's side and it ended up being white so I had to spray it back to hide it. I mounted the metal brackets with black wire tires, some were easier to tighten than others. Hopefully the pics explain it better than I can.