If you want a quick upgrade and don't want to screw with not only having to mess with the driveshafts, the adapter, finding a case then go with the single 4.7. If you want the choice of stock gearing and a crawl option and don't mind reconfiguring the driveline go with dual stock geared which will put you just about at a single 4.7. If you even for a minute think you may want a dual with the 4.7 in the rear case then I'd do it now not later. Having the longer front driveshaft does have its advantages when going duals. Personally I'd go single 4.7.
