I am not sure on the dial you have, that is, whether it should have the "revulator" markings (revs/speeds in gears).
As a 350 it may have had only an 80mph speedo - would have to check this out. My friend that does up speedos for a job would have the specs for the correct dial. I'll see what I can find out if you want.
The twin windows could be correct for this model and even if not, should not be a bother as this is not visible when its in the nacelle and this is how you got the bike.
If you get really stuck on the twin windows I might have a case at home with single window or be able to swap one with my friend.