Breezie - Confirmed its brass. Its 1 1/2" in diameter. Much like you I thought there were only 2 holes but there are 3. Two larger square ones to the left and right of the painter (one looks like natural break but see a 90 degree corner. The third is just below the car and is a more narrow rectangular slot.
I found this a few feet away and at same depth as a 1931 radiator emblem.