Luke - In my info searching, that particular style of "brush grille guard" was offered as an accessory for the 4000 series and up AD trucks, There was a different style/design "Commercial truck" (3000 Series) shown in the first pic below offered on this page from the
1951 Chevy Accessories Manual - Commercial Truck Grille Guard.
The "Utility truck" (4000 Series and up) "brush grille guard" installation instructions for 1951 start on this page
1951 Chevy Accessories Manual - Utility Truck Grille Guard, with the second picture below showing that design installed. To the best of my knowledge these guards were painted black.
The one you have pictured looks like a replica of the original "Big Bolt" style unit with some added touches like the Chevy emblem and "C" and could have been built to fit the smaller "commercial trucks".
Kevin's suggestion on mounting makes sense. The upper support bars would likely pass through the grille and get bolted directly to the frame rearward of the radiator support, perhaps???
