The screws for the top radiator splasher and the speednuts that go on the grille bars, front fenders, and core support aren't your run-of-the-mill hardware.
I picked up several brand-new screws from Gary Thomas at Perrysburg about 15 years ago. IIRC, they looked like an Acme type thread. Can't find anything online in that regard, now.
The OE speednut (P/N 448210) was made of thicker metal, but they seem to break easily.