Yes, we can suppose two where three possibilities, but how to explain this cover clutch which I am going to call "9/10" which has my opinion does not make very serious for the look... We do not have handlebars anymore from now on, but do not be worried because we are going to put a broom!!
Only for it, one can exclude returns of workshop.
It is very difficult to have informations on these Sandcasts.
I think sincerely that there were some also in other countries, but regrettably they were not listed..
Here is a photo of Sandcast E-1014149 and if you look in detail, she also has this famous cover "9/10".
She has her front fender mud before with double cuts and his exhaust muffler " HM CB750 " gets the same music which bewitched that the "HM300"...
And the best it is because she traveled only 2300 kms or approximately 200 miles for you because she was stored and almost forgotten during 40 long years...