The serial number is the tipoff. The A, B, C letter prefix and the location (on the side of the reciever) indicates that this is an "American" Browning made by Remington while the Belgians were hosting uninvited guests 1940-1945(6).
It will have the magazine cutoff, but another tip is the safety location. The crossbolt behind the trigger type was not introduced on FN Brownings until the early 50's.
The American Browning is pretty much a Model 11 and the parts will not interchange with the FN A-5's.
Still cool guns, and an interesting historical note.