Agree with above poster, it is a mismatched or crudely forced match. That is a civilian-proofed barrel placed in a military wartime slide and frame, even has what may have been the wartime locking block transferred. The civilian proof stamp gives it away, as well as the 2nd grade shop project serial stamp.
But all is not yet lost, there is a possibility of it being a postwar made barrel for one of the AB9 series, or taken from a police issue. Much more can be learned when better pictures are available.
I can only recommend, after sad personal experience, that you forgo using the wartime slide and instead get a P1 fat slide (with P1 internals, there are a few key differences) to make it truly a shooter. The wartime slide can crack and the locking block can give way, and even though it would not be a collector piece lost, you could be injured in the aftermath.