George,
There are several variations of the cars over the years. The changes over the years are as follows:
Steps - riveted to frame (typically brass), spot welded to frame (painted the same color as frame), new frame with steps as part of frame
Labeling - 3210 & American Flyer plates, all American Flyer plates, all decals
tank support finish - it varies
tank ends - they vary
domes - brass or nickel
I posted all of the 1928 through 1937 tank car variations in last weekend's tinplate photos, so review that for the various configurations.
NWL