I can give you outside dimension of grille for the left & right speaker is approx. 4 1/2" from windshield and 5" wide. Grilles are screwed in and impossible to give you how the grille screws are positioned. I don't remember if the grilles had studs or use screws to secure them. Probably did it 30 years ago but car came with 3 speaker dash.
View attachment 70926 3 7/8” + -