You are right that it is Mark Kingsworth's design. And it is an excellent one at that. I never said that the ship was Roman's design, only that it was his IMAGE design. Perhaps that was a poor word choice on my part.
We attempt to get permission for the use of other people's art in our fan-fiction sim. As I recall, Mark Kingsworth was contacted personally about the use of this craft.
Most Trek fan artists have no issue with re-use of their material. In fact, they usually encourage it. I would! To use their material indicates the highest level of appreciation for the work that they invested in the project.