Some of the early Fords have the axle stop mounted on a hollow metal base. The metal base rests against the frame and has a notch cut in the metal base so that it "clears" the rivet that is in the frame thereby allowing the metal base to sit squarely on the frame.. My 40 Ford has that. I do not think you have that style axle bumper. It's nothing to worry about. Bob Drake shows he has axle bumper for your car here:
https://www.bobdrake.com/FordItem.aspx?Item=51A-3020