6-17738 NORTHERN PACIFIC X-31
Car is not as advertised in the catalog.
SIRT
That is true. The decoration of the 6-17738 was changed to make it prototypically correct.
The ex-DT&I 40 foot round roof cars were built by Greenville Steel Car in 1937 and leased to the NP by A.A. Morrison in the early 1960s. These cars never received NP Monads. They were numbered NP 39000-39335.
The NP also leased 50 foot round roof box cars. NP 39500-39609 came from the DT&I and did not receive Monads. NP 39610-39759 came from the N&W and were the only round roof box cars on the NP that did receive the Monad herald.
As Ed noted the first photo you posted is of a 40 foot car. It is an ex-DT&I car and does not have a Monad. The Lionel car is correctly numbered and decorated for a prototype car in this series.
When weathering this car take note of the upper left of the car in each of the pictures that you posted. The 50 foot ex-N&W car has the Morrison ownership stencil. The 40 foot ex-DT&I car was purchased by the NP after the expiration of the lease and the stenciled markings have been patched over.
For the price, it at least should have come with the interior box load.
For a loaded car coming off of the NP that wouldn't be very prototypical. They were leased specifically for lumber service and typically assigned to the car pool out of the NPs Auburn yard. It is unlikely that they would be diverted to general merchandise service with an eastbound load. The NP had strong demand from lumber shippers for double door box cars in the early 60s to allow forklift loading. These leased box cars were a quick and inexpensive way to meet that demand.
After the cars were purchased some were placed in green veneer service with the doors removed and stake pockets added to secure the opening. These lasted in declining numbers into the BN era.