You need to go to the Dodge web sight to get this answer... there are a set of specific wheel bases available for each of the 3500, 4500, 5500 C&C in each Cab configuration... Do you want a 2WD, 4WD, regular cab? quad cab? 3500?, 4500? 5500?
My new 5500 is a standard cab 2WD with about 13 ft from the back of the cab to the end of the frame rails...
The web sight has the back of cab to end of frame rail dimension. .