For what it's worth, I believe that the Athearn RBL uses the old Details West tooling and is something like 3" short. I have one of the Details West cars and four of the Atlas, all repainted and lettered for WSOR. I read on another discussion group about the "discrepancy" and had never noticed the difference even though I usually run the cars in groups of 2 or more. Anyway, it's not enough of a difference--at least to my eyes--to matter.
John Timm