This is a free-lance 24' Narrow Gauge Flat Car (Nn3).  It features a simulated wood deck with nail heads, stake pockets, stirrups, queen posts for wire (or thread) truss rods, and underbody brake cylinder.

To complete, it requires one (1) pair of MTL Z scale trucks with couplers (truck-mounted), an N scale vertical brake wheel, and thin wire or thread to represent truss rods.