For plastic grills, make a paste using bits of abs and acetone.Bevel all cracks or repair sections and apply evenly.For large gaps additional application may be required to build the area up.Allow 5 or 6 days to cure.
The repair can then be easily sanded and shaped.Now it's just a matter of masking sections off and finding matching paint. I believe Mopar Muscle Wheel paint is the match for most satin argent grills.
If you are doing a Sharktooth grill be warned masking and painting the fins can be an 8 hour ordeal and is very tedious!