IPMS Stockholm lists that brown as FS 20117 with the comment - used on Nell, Betty, and Claude. Just in case you do not have a copy of the FS color fan deck or color chips, it is a medium reddish brown, not unlike the brown primer used later on props and spinners but not as red.
If you can't find FS 20117, use the red-brown primer. Most paint manufacturers offer this. Close enough for government work!
Pete