Yes, the pickup grilles are smaller than the Big Bolts. You are correct that no one reproduces the Big Bolt grilles unfortunately, so finding a donor truck is the way to go.
On a good note, pretty much any of the Chevy Big Bolts 1947-53 like yours, with the exception of COE's, use the same grille. They are usually lesser in demand, so perhaps easier to find.
Best of luck in your search.
