The inserts I build for the 1939 Coast to Coast mount from the inside of the hood side panels/grille shell. You will save the 3/8”-1/2” recess in the molded grille opening, but trim off the original mounting flange around the entire opening.
I have a pair of their grille panels here at the shop.
There are 5 mounting tabs on each grille panel, 3 along the bottom and 2 at the top/center.
3/8" spacing between bars:
front polish with satin sides $1295
fully polished $1495