I'm not sure the brackets are different, I wonder if the rubber bushing that surrounds the leafs are different between the 4 leaf and the 5 leaf.

Or, now that I think about it, I'm not sure the 4 leaf didn't have a short spring or spacer about the same length as the bracket, so Mopar only needed one set of brackets and rubber bushings. Chrysler was going broke at the time, a short piece of 1/4" thick 2" x 6" steel with a hole punched in it would have been pretty cheap. Gene