I agree. A good bike to start with.
That is also a way to fit your rear numberplate holder without moving the contract plate....
I think most of the missing parts can be obtained in this forum.
What makes the age of a motorcycle?
I personally would say that the frame determines the age.
The engine can be changed anytime, replaced by an older or a newer one.
Within the army system, its more likely an engine was matched to a frame if and when the original broke down, and not the other way around.
I harldy believe they had an engine and wondered: "where can I find a frame to mount it in".
With this criteria,
This is a 1941/42 bike with a rather old engine in it.
Certainly a nice starting point for a full military restoration.