If your asking about body parts they are the same. 4x2 vs 4x4 when it comes to converting you have differences. I forget if the frames were exactly the same or if it was just drilling holes. There is a difference in the F250 4x4 used a twin I Beam 4x4 the F350 4x4 used a Dana 60 straight axle. The 86 F250 4x4 used a plastic radiator & I believe the F350 4x4 used a brass radiator.
Craig