Generator ID

[DD931]

I just overhauled the generator for my '48 F-1. The case is stamped with a Ford script followed by C-2. I also have a core I picked up somewhere that I plan to overhaul as a spare. I assume it's from a car, because it has a narrow belt pulley. No idea where it actually came from. In every other respect it seems exactly like the one on my truck, except the number on the case after the Ford logo is 9-1-1. Does anyone know what these numbers mean?