Firdt obvious sign of an early one is the sticker on the side panel under the 500 Four badge that states
Honda Motor Co.,
Tokyo Japan.
there were press models and i have seen one about years ago, if you can find pictures you should find registrations.
The first Japanese ones had fixed footrests, a light in the steering stem top nut and several other mods from other markets but officialy only K1 models ever came to the UK, even whilst US had a K2