Craig,
I have both a 37 car and a 37 1/2 ton. I just measured the grille as best I could (they're both installed, so I couldn't get to the real edges of the grilles because on both top and bottom they sit in a recess. The amazing thing that I discovered is that the center height is VERY close to being the same height, i.e., 29 1/2 inches (probably your 30" would be correct if out of the vehicles). It's possible that the truck grille could be another 1/2 or 3/4" inch taller, but probably more like 1/2", if that.
The big difference, however, is in the width. I measured across the grilles at the furthest point, i.e., toward the top, where the grille flairs out to a point on each side. The car grille measures approximately 21" tip to tip, while the truck grille is approximately 24" tip to tip! So, the big difference in the grilles is the width, not the height.
I hope this is helpful.
Jim