I finally got my 2 keyboards from the seller- both are filthy and nasty. The first, as expected was a regular old 1391401 that seems to have a good key feel and be in good shape, despite all the dirt.
The second is a dell-labeled 52g, and it is very yellow for a Model M. I didn't even know they could yellow like that. Maybe I will try a retrobright experiment on it or something.