I'll let Doug confirm the model, but looks like a Mistral to me. If this is the only number on the BB then I would think it is an early 4 digit number from the 60's. Sometimes you find odd 3D numbers along side/as well as the actual frame number. Is it possible to confirm the presence of any other markings? Also that oiler on the bottom of the BB is a bit odd, could it be a CB frame/number painted up as a Holdsworth? Looks like it has run a front gear change too at some time.

A number this low would be from around 1962, but the mistral didn't start until 1964. However we have seen frames with numbers on that are too low for a particular model before which is leading us to believe we are seeing some early prototype or marketing frames being built well in advance of the model launch. A couple of years has been seen before.

There is a track frame described as a Mistral in this group, #1089 from 1964, but the seat stay is not wrap over so not sure exactly what that one is either. Think a bit more input is needed to fully ID this frame.