Slide the pivot ball as far back as possible- - - - -it should move at least a couple of inches. Most likely, the missing bolt is wedged between the U joint and the Okie bushing, which is keeping the joint from sliding back far enough on the spline to clear the transmission housing. Supporting the frame of the truck on jack stands (not the axle tubes) so the rear end hangs free will minimize the down pressure on the torque tube. Worst case scenario, unbolt the spring U bolts and slide the whole axle assembly back on the springs. Then you'll be able to drop the torque tube down and deal with removing the U joint.
Jerry
