Will a 1972 Chevy van grill fit on truck?

No, a 1972 Chevy van grille will almost certainly not fit on a truck. Trucks and vans have completely different body styles and grille dimensions. Even if you're talking about a Chevy truck from the same year, the grille openings and mounting points are significantly different. You'd need extensive custom fabrication to even attempt it, and the end result would likely look very awkward.