In the 50s and 60s era coaches wit only a top rail the drapes are normally held to the wall by adding a ring to the back of the drape 3/4 to half way from the top. The windows likely have snaps at the proper heights on each side. Then there was a cord run through the rings and attached to the snaps. This allowed the curtains to move, but did not impede the view as well as holding them to the wall. I have see the fine window screen spline used as a cord since it is slightly stretchy and will take the heat.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato