I need help identifying the correct channel balance for my windows. I thought I needed the Series 751, but as you can see by the photos, mine has a screw hole at the top of my balance and it has a plain channel with only one (not two) sash cords. The shoe from the S-751 looks to be correct, however. Can you please help me out, as I must return the incorrect part and get the correct one for MANY windows. THANKS, Martine Mickiewicz