Well it appears the arms are symmetrical despite the different part numbers listed for the OEM bushes.
Interestingly, the whiteline and similar aftermarket bushes are the same for Left and Right which implies symmetry.
I took it off the car and they are geomtrically the same except for the side that has been machined flat. It appears to make no difference to the operation of the arm but my guess is due to manufacturability. e.g. Mistubishi not having to cast a left and right set. Correct me if im wrong.
Either way, my findings is that they are interchangable and symmetric. Its on my car now, aligned and works just fine.