The parts book lists different bushings for the front of the rear arms & since GM only supplied the arms with bushings,the book lists 2 part #s for the arms also. 442,vistas & police take one bushing (probably a stiffer HD bushing),regular F85/cutlasses take another part #. I don't think there is a difference in the actual arm itself,unless the car was built in Canada. The parts book lists a different upper arm for the Canada cars that came with chevy 12 bolts. All the parts vendors seem to sell just one bushing that fits all locations on the rear suspension.

 

^^^THIS.

The stamped metal arms are the same for all Type O axles, but the different part numbers are for the arm assembly that includes the rubber bushing. The 442 used a stiffer bushing from the factory. Unfortunately, the replacements are all the same.

 

Did any Oldsmobile's with the FE2 suspension (i.e. 442's) get the rear upper control arms with the additional reinforcement? See pic below.