Your 83 will have a 22r and a 5 speed you will not be able to swap with the 20r 4 speeds since that would be downgrading. Some wiring will be different from year to year, axle housings, gear ratios, will also be different. They made a lot of changes 79 to 83 bringing the truck to what it became for the next decade. The body was pretty much the same 79 to 83. The drivetrain on an 83 is more akin to the second gens than the 1st.