The Mantua "Heavies" model is the only one I'm aware of, but there

may be

another one out there.

Though I'm late to this party, there's still something to add. I
guess
you mean that the Mantua cars are a good starting point for a kit
bash. The H- series cars had an unusual end arrangement. It was
similar to a conventional hopper, with the slope sheet and slope
sheet
braces visible. However, the end panels of the sides were sheathed.
Viewed from the side, the cars look like conventional gons. Viewed
from the end, they look like conventional open hoppers.

I don't know if this feature was part of the original design, or
added
at the time the cars were rebuilt.

Jerry Dziedzic
Pattenburg, NJ