About the stripped grip screw - I have to wonder if someone has tried to replace the inch pattern Inglis grip screw with a metric FN? If so, I suspect there is a good chance that the frame screw hole is stripped, or at least cross-threaded as well.

Clive Law's book, "INGLIS DIAMOND; THE CANADIAN HIGH POWER PISTOL" list's your serial number as within the July 1944 production.