there are some minor differences earlier on, depending on what you want to do. the biggest is the change in the radiator area from 86 to 87+ the rad supports and hood latches changed. these (plus the firewall got a bit of a bump in it) were done to clear the new 4.0 engine going in. oh, and in 91 they changed up some of the front fascia/grill pieces and how they went together.
there are some differences in the rear frame between shortbeds and long beds.
that's all I can think of with respect to the body. these trucks are like lego. you can get a solid body and make it into the trim level you want if you can find the right pieces.