Seem to recall it was an old airfix series 1 'dogfight double' which was the Red Barons Triplane and an Avro 504K I think. Didn't they used to be supplied in a plastic bag?
I've made many since and still make the occasinal one now having just spent 18 months living in during the week.
I still have an unmade Airfix 1;72 scale Hercules kit from around 1975. Still in its original box and it came complete with the Bloodhound Missile kit. The aircraft decals are for XV196 in its desert brown with the white 'sunroof' and no refuelling probe. Looks a little different these days with all its lumps and bumps. Wonder if this is a collectors item yet.