Armand,

An easy way to add a Monon car from that era is the '37 AAR  9000 series car that the Monon Society had Red Caboose run.  Caboose Hobbies is now the vendor for the Society models:  

https://www.caboosehobbies.com/

These models are decorated in the as-delivered early 1940s scheme which will work for you, but they were also painted later in every other scheme the Monon had, including the white stripe.  Mont did detailing articles for them in (I think) Mainline modeler.

Regards,

Mike Aufderheide