Nice score! I've got one of those that I just got back on the road a few months ago. They seem small in person but they handle well and don't seem like it when you ride them around. Definitely turns heads.
Looks like you have at least one side cover on the engine which is cool. Those seem to be rare these days.
I'd be interested to know what carb / sprocket / version you have. I think most of the HS50's were 25mph bikes, maybe?
What's wired up on the back? Did it have turn signals or something? I found two extra wires on the back of mine in the fender area as well.