Why don't you try the 2-part epoxy called "PC-7"? It mixes easily, doesn't make deadly fumes, and only costs a few bucks. You can usually find it in any hardware store or autoparts store. Just follow the directions, and "open up" the crack in the grille to give the PC-7 a larger surface to adhere to. I have used this stuff on my 1971 'cuda grille that had about 4 or 5 different cracks. I have also used it on steering wheels and other hard plastic parts. It worked great, cured within 1 day, and was easy to mould into shape and then sand to a smooth finish. Good luck.