The top sash guide is rectangular in shape and not tapered, the measurement across the top is (photo 1) 7/8" wide and 1-1/8" in length. Inside window channel (picture 2) 1" in length and 5/8" in width.
Bob from SWISCO responded:
May 20, 2021
Start by looking at our 18-174 Top Sash Guide. Look over the dimensions and see if you think this could work for you.