At first glance, i don't see any issues with it.
It looks like a common 1914 to me.
There are examples of ww1 cores in ww2 sized frames.
Easiest way to check is to simply hold it next to one
of your 1939 crosses.
The core design is the "slant W core" used by several different
The mark looks to be a "R". Possibly Alfred Rosner