Where would you even put the Cummins? In the back? I'm pretty sure it's at least twice as big as there's space for up front, plus you'd way overload the front axle. If you really want a Cummins sprinter probably the only way is to drop the body onto a pickup chassis.
Vanislevan, I don't blame you for asking but I don't think anyone here has done anything remotely like what you are thinking of. Pirate 4x4, Expedition Portal or maybe the Sprinter Source might be a better place to find advice on unusual Sprinter conversions.