Thanks for posting! I agree with you; I believe that you may have the Andersen Straight arm Operator, 9-3/8". As for which side it could be,the best course of action is to simply compare each arm you have to whichever picture matches it on our site. You see, manufacturers name their operators "Left" and "Right" in an almost arbitrary fashion. Some manufacturers imply that the operator is located on the right or left side, while others imply that it opens the window to the right or left, respectively. There is no industry standard.
Like I said, your best bet is to simply compare your hardware to the pictures on our site and determine which arm is which that way.