UPDATE 11-9-20 I purchased the Roadrunner Grille Insert from Greg Wann , they are really nice and Greg is a great guy to deal with ! The inserts are designed to fit the Monogram 1/24 scale grilles so I had intended to modify one of those to fit the 1/25 body , but then realized to was much easier to fit the insert to the MPC grille .
The plan is to file a recess in the MPC grille .
The insert was carefully located then some CA glue was used to attach it permanently .
A little trimming and it's done .
I painted the grille Dark Argent with a black wash and Light Argent was used to accent the headlight openings . The Roadrunner was a real pain and took two tries to get it decent .
Next I mixed a dab of white with some clear and painted the molded headlight lenses .
And here's the finished grille ! The overhead light is reflecting off the paint , it's actually much darker than in the photo .