From what I understand, the "H" designates a 4 valve head, and the "C" designates custom. As for the physical differences, I'm not sure. I believe that the AMT Freightliner kit has the NHC 250. You could probably pick that whole kit up as cheap as you can buy a resin engine. Some of the short hood trucks tilted the Cummins, leaning the engine toward the passenger side, but I'm not sure about the Dodge. Most of the Dodges that I've seen had Detroits. You may also find some help on Hank's Truck Forum, there are a lot of knowledgeable guys over there. Hope this helps. Brian