From 85-87 the front lower control arms are made from 2 pieces of stamped steel, where-as the 84's are a multi piece boxed structure.
Whether 2nd design is stronger than the first, I can't say. I'd think they switched to the stamped method simply due to a lower production cost over the multi pieced welded ones in 84.
The only down side I've ever seen with the 84 lower arms is that the boxed structure can collect water, mud, debris, etc, and not drain properly. Due to this they can rust out from the inside out leading to trouble down the road.
