Compared to other conversions from 2wd to 4wd, converting a Ram 5500 C&C should be easier because the Ram C&C platform uses some 4wd components as factory equipment on 2wd units.
The frame and suspension components are all 4wd and the ride height of a 2wd C&C is the same as a 4wd.
The front axle assembly of a 2wd C&C is a modified casting that uses a 4wd axle assembly with what appears to be the differential housing cast in but it is a dummy, a differential couldn't be installed.
My guess, and I empathize guess, is that you could buy a 2wd C&C, jack up the frame, and remove the entire 2wd front axle assembly and simply bolt in the 4wd front axle assembly.
Of course you would be forced to purchase a long list of very expensive components including front driveshaft, transfer case, mounting brackets, hardware, and lots of electrical/electronic control modules, and harnesses.
The engine may use a separate and distinct ECM or the PCM may be different.
I don't know if the Aisin is interchangeable between 2wd and 4wd or if one has a special casting.
The conversion is probably relatively easy to accomplish but the components would cost a fortune unless you got lucky and found an identical wreck in a salvage yard.
My unsolicited advice is the cost wouldn't be worth the reward.