There have not been any Lionel O Scale FEC 50' Modern Boxcars and FEC Double-Door 50' Boxcars.
Florida East Coast has Greenbrier All-Purpose Stack Cars for Intermodal Containers that have not been produced in O Scale.
Florida East Coast had 45' Trailers and 89' Flat Cars that could be produced as a set by Atlas O.
FEC 7204 is a 53' flat car like the PS-4 flat car made by Lionel.
Andrew