I looked at a lot of Speedtwins for shocks, forks and that oddish side cover and the only ones that look right are circa 1956. It's the right side instead of the left but what do you think?
http://www.bradsbikes.net/view_photo.aspx?maxWidth=500&photoID=845


A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)