The price doesn't seem bad. The mag shown in the picture could very well be an original with the black bakelite/plastic base which would be correct.
Blue is original, if I was you, those photos would be take on my kitchen table. The mag isn't an issue either, by 1942 it would have been issued with a type 4 fxo magazine. Almost all byf 42s were issued with black bakelite mags.
Which letter block? 42 was the last of the Obendorf P08s with the transition to P38 production.
The later blocks were contract exports to Portugal and Romania, not to the German army (heer).
From Published production docs and Datig book it looks like the following for the Army with the last ones accepted in the L block. Last order was K block. And I do see many on the Jan
still Luger Forum in the 9000 serials in the K block.
M and N (1943?) were exported.
Dec 42 M 4000 port
Nov 42 L 1000 heer accepted, not ordered
Oct 42 K 3218 heer
I can't make out the serials with the low res pics.
"Those were the days my friend."