I HAVE A 81 F150 2 WHEEL DRIVE AND A 83 F150 4 WHEEL DRIVE. THE 4 WHEEL DRIVE HAS A RUSTY BODY AND I WAS WANTING TO SWAP THE RUNNING GEAR OVER TO THE 2 WHEEL DRIVE. I WOULD LIKE TO KNOW IF THE FRAME IS THE SAME ON BOTH TRUCKS? I THINK CHANGING THE RUNNING GEAR WOULD BE EASIER THAN SWAPPING THE BODY. ANY HELP WOULD BE GREATLY APPRECIATED.  

You'll have an easier time changing bodies than drivetrain.  Mostly depends on the frame condition of both.  If the 4x4 has a crappy frame then move the running gear.  Just be aware that moving the running gear is going to require alot of fab work.  The frames should be close to the same, but suspension attachments and possibly motor mounts are all different.  Start measuring before you start hacking stuff out.  Remember to check drivline and tranny/t-case clearances.