Does anyone happen to know when the T&P started to replace the paneled wooden doors on their heavyweight baggage-express cars with the more modern looking ply-metal doors that are featured in published color photos?

I note that in the SPH&TS’ book on front end cars in their passenger car series, there is a B&W photograph of two T&P heavyweight baggage-express cars heading up a west bound Southern Pacific mail train. Both cars have paneled doors and clerestory roofs. The lead car sports the Eagle paint scheme while the other is in the old “Pullman Green” scheme. The photo was taken in 1951

The reason that I’m asking is I’m starting to create an early 50s version of the Louisiana Daylight in N Scale and would like the two baggage-express cars that headed up the train to be as prototypical as possible. The upper part of the doors would have been painted blue, which is much easier to mask on the ply-metal doors than on the multipane, paneled doors.

Diane Wolfgram