Illinois RR Museum, Pullman Library could have a WP PS-1 picture.
1951 is just out of my 1950-modeling/collecting scope, but you could ask them.
The 1937, 1945 and 1947 batches were all built by Mount Vernon, or am I missing something?
Weird thing is that the 1936-built WP 19001-19050 double door car has black ends according to the stencilling instructions, but clearly has red ends & roof on the Sacramento builders photo.
cheers, Fred Jansz