Well, there's no doubt that it is plain gauge Reynolds 531, based on the post size. Also, those are the remnants of a Reynolds decal. The component mix is interesting. It has the Valentino derailleurs of a 1974 Olympic 78 model but the Sugino Maxy crankset of 1975. The seat tube decals are typical of 1974, so perhaps they introduced a crankset change after the 1974 catalogue was issued? That might explain the colour difference too. Personally, I'd have no qualms presenting it as a mid-1970s Falcon Olympic 78.