Mario help us out a little and tell us what your truck is...
If it's a torque tube its most likely a pre-'55 1/2-ton. But answering the which rear question really depends on what year the truck is. Pre '47 the answer is different than '47 - '54.
If your truck is a '47 - '54 you can replace the pumpkin with one from an open drive truck but more important is that the torque tube axle pivots on the frame and you need to eliminate that pivot to switch to open drive.
