A box car includes end walls joined to opposing side walls that define the interior cargo area. Each end wall includes a corrugated side that faces the cargo area. The adjustable spacer is arranged within a cavity in the corrugated side in a stowed position so that it does not protrude into the cargo area. The side walls include tracks in which opposing guides that support the lateral beam are slideably received. The tracks do not protrude into the cargo area. The guides include multiple holes providing keyways that receive removable locks. Vertical side posts are arranged along the exterior of the side walls. Holes are arranged in the side walls in the area of the side posts. The locks are received in one of the holes in the guides and a hole in the side wall to lock the adjustable spacer in the desired position relative to the box car.