You can run front-drive only, but not for great lengths of time. It just was not designed for it, especially for everyday driving. On a NP203 you would have to shift into Hi-Lock. The transfer case is designed to split torque 50/50. If you remove one of the driveshafts, the T-case will have an unbalanced load. This will eventually cause abnormal wear and a clunking noise (bad!). A NP205 is stronger, but chances are you will destroy front end parts quicker than the T-case.