It's a close call. You want the washer that has the axle with the flats vertical in a horizontal dropout (90° turn). Washers 5, 6 & 7 re of the right type, so it's a question of angle. I defer to dan's expertise, but just eyeballing it in the photo, I think the angle of #6 is too far off, and 5 or 7 would be closer. Note you can also fine tune the angle a bit by flipping the tab front to back, or reversing the left and right washers.

It would be nice if they gave you the actual angle from horizontal they were made for, or at least the actual angle of turn.