Just finished this lovely little tank car for a client. The kit is made by Precision Scale Company, and is offered in the catalogue as a HOn3 UTLX frameless tank car, but is easily upgraded to a standard gauge car. Some adjustment with the couplers and a larger K brake cylinder and reservoir and your set.
Add in decals from Speedwitch Media and what more could you ask for?
It's funny from an historical point of view, the frameless concept was resisted by the railroads for some time in the early 20th century and today that's all you see.