Jerry, Celanese never owned its own tank cars and, as far as I know, they leased exclusively from General American.  At least, all of the 10+ photos I have of Celanese cars show them to be of General American design and bearing GATX reporting marks.  So I'm sorry to tell you that the IM model is almost certainly bogus.  Also, BTW, most (though not all) Celanese cars were insulated and many of those cars had dome platforms and railings.