50' ACF Exterior Post Boxcar - Ready to Run -- Southern #17854Details: Serve shippers on your HO railroad with these WalthersMainline 50' ACF Exterior Post Boxcars. Responding to a growing shortage of serviceable cars, ACF and other builders unveiled a new generation of bigger equipment in the 1970s with increased width and height to improve carrying capacity. Today, they're still in service for Railbox and many other roads, where they can be found moving all types of cargo. Features of these models include: One