Honda-SOHC

I know this sounds daft but my bike has 550 frame and exhaust but a 500 four motor and badges. It was hardly used when I bought it ten years ago and while it might be a bitsa it looks like it has always been like this rather than been bodged by previous owner. Someone told me it was an Italian import so don’t know if they made a few like this for other markets? Anyway it’s a great bike and I’ve had lots of fun but I’m just curious...Can anyone enlighten me? Will post pics when I can
https://imgur.com/a/p8Sf0