The short-door car side screens are even flappier than the later ones, but there are some quite nice steady braces available from Librands which go inside the doors and provide a bit of triangulation.
They work pretty well, I fitted a set back in the winter and they certainly improve matters.
For the long-door cars I think the later rubber windscreen seals are probably better, always assuming one's side screens have been properly constructed to fit into them...
