Because the 1/2 ton truck rear axle used a
Torque Tube Axle, .
and I believe the 3/4 ton truck is longer than the 1/2 ton truck.
You would have to use a
Non-Torque Tube Axle and flipping the 1/2 ton springs.
If the 3/4 ton truck is the same length as the 1/2 ton truck, all you would have to do is find a tranny with a torque tube tail housing.
You should be able to disconnect the 1/2 ton leaf springs at the frame and reconnect them onto the 3/4 ton truck frame.
What year make model are the trucks you have?
