It was recently brought to my attention that awhile back on this list, it was asserted that some SP steam-era tank cars had 60-inch diameter domes. (I did not catch this in passing.) I have just checked drawings for O-50-9, O-50-12 and O-50-13 cars, and all had 54-inch diameter domes; photos confirm that these cars were all very similarly proportioned. The Tichy "large dome" part is 60 inches, and thus in my opinion cannot be used to correct the dome on an Athearn tank car, though it may provide the correct height. The Athearn dome, on the cylindrical part, is only about 10 scale inches high, and ought to be about 21 inches.
All the cars mentioned above had nominal 12,500-gallon capacity. The Class O-50-14 cars were 8000 gallons and appear to have similar if not smaller domes. If anyone can provide more (or better) information, I'd be delighted to hear it.
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