[Model51]

Attached is an image from page 350 of the Green Book. It features a 1939 Truck front end, not the 112" Commercial version. Is the part you are seeking? I don't know what the difference is between the truck and commercial models, but there is one.
If you are working on a 112" panel delivery then the part number is 81C-8298/9 but if you are assembling a 134" panel truck the part number is 81T-8298/9. I only mention this as these parts are different for the two different "panel" applications.

I think this part may be symmetrically opposite of the one on the other side of the radiator? If you have the one from the other side, then that might be your model.
It also looks to be a formed part, flat on the radiator side, but dished like the grille with a rib on the front side, so it could involve some metal shaping if you have to make one from scratch.