At the rear, outboard end of the swingarm there is a design difference described as "anti-squat", it can be found described in the 126 Body and Chassis FSM. I suspect that is the fundemental basic difference between the standard swing arm and the aluminum versions found on 126 coupes. How does this difference manifest itself as far as what will fit and what limitations on parts that connect are not known to me other than the differences exist. Good luck!