Jason:
I also have a 1947 T35. I'm located in Nova Scotia. I have photos and dimensions for the missing toolbox you need and although it is not surplus to my needs, I have the cast aluminum transmission output drive cover, which would be easy to duplicate in fibreglas. I can also send you detailed photos of my bike which is mostly, but not perfectly correct.
Where are you and where did you find a Douglas in Canada?
David Aggett