As pictured above, these cars are available with either offset sides or ribbed sides.
Here's what Bluford Shops has to say about them -
70 ton 3-bay offset side hoppers first appeared in the late '20s and by the late '30s had become an AAR standard design with cars being delivered from a number of builders in large quantities to railroads across the country. The last of these cars were delivered in the mid-'60s and many remained in service through the '80s.
The AAR had a standard 70 ton rib side hopper as well, however New York Central made changes to the AAR design in 1956 and their variation became popular with more railroads than the AAR stock standard! These cars were lower and shorter than later 90 and 100 ton cars but had more ribs (making for 14 full length panels.) Thirteen of the fifteen ribs were welded in place instead of riveted. These cars were built by a number of builders from 1956 through the late 60s with many serving through the 1990s and perhaps beyond...
These cars are also available with wood chip side extensions (either flat or ribbed) -
Beginning in the late 50s, wood chips went from something to be disposed of to a valuable commodity. Since wood chips are less dense than coal, gravel and other hopper loads, many railroads added high extensions to standard hoppers for this service. The extentions were simple affairs, either rib sided or flat sided that were welded to the top chords of standard hoppers. These N scale models come ready-to-run with knuckle couplers, loads, and are equipped with Fox Valley Models metal wheels