Thanks for all the input. Here's what I have learnt so far:
The upper is a 1908 First Issue made in 1909. All matching except for the firing pin, which might be Swiss. The magazine is Mexican or the like.
The frame is post-1913 apparently. What tells us that? It is NOT an Alphabet Commercial. No Mauser hump. Grips are matching with last two digits to frame. It is a 4000 series "a" block with multiple inspection marks. The recoil spring has 19 coils, assuming it is original, means it is a 9mm frame. Anyone like to take a stab at when it was made and by whom? WWI military? Artillery frame perhaps? Made by DWM or?
Thanks again everyone.