I dont know alot about the axle/wheel side of things but....
If you have a long box then you can just swap the box.
If you have a short box then you have alot of work to do it. Short box dually never existed from GM/CHEV therefor you would have to have a custom bed made/modified and I think it would look pretty silly.
I saw a pic once here. Someone has done a shortbox dually.
Do a search for "dually conversion" in the "exterior" section