I believe the USNS Ro-Ro conversion you can make of the Imex NedLloyd Rouen kit is of the Cape K class ships, Cape Knox (T-AKR 5082) and Cape Kennedy (T-AKR 5083), not the Cape H class. The most obvious visual difference is that the H class has the big handling crane for containers on the foredeck, while the K class does not.
Cape Knox is the former NedLloyd Rouen: http://www.navsource.org/archives/09/545082.htm and is homeported in New Orleans. This is a conversion I am interested in doing as well. I have the Imex kit and am now trying to figure out how to make/buy 1/400 scale military vehicles for the deck. Right now I am thinking about converting 1/285 wargame vehicles... a jeep in 1/285 is about the same size as a humvee in 1/400.
And the Cape Knox doesn't have any weaponry on it, either.