Hi Lettice,
From your photos, the boat would appear to be what is known as a Gaff Sloop Rig and so it is unlikely there would have been a small sail between the upper part of mast and the gaff yard supporting the mainsail. If you Google it you will see lots of images.
As Ashley says, it looks to be pretty much all there and just needs some setting up.
Does the model have an interesting history?
Colin