Due to the curve of a front bumper and assuming you had correct rear brackets with a front bumper, the brackets may have been "adjusted" somewhat to fit the curved bumper. I'm not sure if the hole spacing is the same, but keep in mind that the 47/48 bumpers were a lot more rounded in the vertical dimension and look like car bumpers. Also note that the correct 53 rear bumper has the same curve as the front in the vertical dimension, but the rear is shorter and does not have as much curve on the ends as the front. Rear bumpers were not that common originally, and I still wouldn't be surprised if you have car brackets on your truck. Do you have any pictures?
