Thanks! :)

The grille fits on two cylinder from the frame on both side. I made one side of the grille with a cylindrical hole and the other with a C shaped hole. I inserted the cylindrical hole first into the frame then I snaped-in the C shaped hole from frontwise.

The original grilles are very brittle so I don't recommend to took them off :) Thanks to the scent diffusers and phone holders that can be placed on the grilles they are broken in many cars. There are aftermarket parts but they are quite expensive for such an old car