AHM did not make a stockcar. the original Atlas O scale had a stock car. The old original Atlas from the 80s are slightly better detailed in my opinion than the AHM cars of the same vintage. I think you consider them to add some variety. AHM did the boxcar, reefer, Flatcar and 40 gondola that I am aware of. The boxcar is a low height car like the ARA 1923 design or the Pennsy X29. Atlas O did a sliding door boxcar, plugdoor boxcar, 52 ft gondola that I am aware. The Atlas Boxcar is a slightly newer 1930s era prototype that is a little taller (1/4 inch) than the AHM car so it is nice variation. The prices should be about the same. The Old Atlas may be a few bucks more per car.
You can get quite a bit of industrial switcing in an area like that I think depending on how much you can use.
