In 2003 K-Line started making S gauge cars using the molds/dies from the old Marx "3/16" scale cars. The run on a new design sprung diecast truck. There were a total of 42 different cars made plus some special runs for advertisers. These cars are usually available on auction sites.The S gauge OB's are distinctive, they are purple and yellow.
Those Marx molds were not 3/16" size. They were from the Marx deluxe plastic line, which is larger than true 3/16" size. That's probably why they did not sell as well as K-Line would have liked.
In general, American Flyer operators are much fussier about keeping to scale sizing than post war three rail operators.
Marx 3/16" size cars are almost all tinplate, with the exception of a hopper, and maybe a closed door boxcar and a closed door stock car, all in the basic plastic (non-deluxe) line.
The trucks look like those made by American Models.