Bump.
The owner is "97% sure, this is the original engine from this frame". CB500E 1032045.
The frame number does not appear to be an overstamp, and there is no sign of tampering with the original number, if there was a different one, that is. It doesn't seem likely that one would overstamp an original frame number if the bike was stolen and recovered; what would be the point? A pre-production frame seems most likely, but the engine number doesn't seem early enough. No-one able to decipher the Japanese script?