Pemco made a 53-foot flatcar with riveted fishbelly sides and 16 stake pockets. The thin portion of the sides above the trucks extends a bit further inboard than most designs. Does this car have a prototype? Trying to add some flatcar variety to a friend's layout.

Here's a page with pictures of the model:

http://tycotrain.tripod.com/pemcorailwaysystem/id8.html

Scott Chatfield