Yes - the Aluminum based extruded blued steel magazine (by Haenel) is from a later era. It's from the late 1930s through 1942 period.
There is normally a hole in the frame for mounting the trigger. This one may have been drilled out as it appears slightly larger than normal.
Your take down lever has been snapped off.
The stock lug would be at the bottom of the rear frame strap near the magazine well.
Yes - the stock lug is used for attaching a carbine stock. See
this site for pictures.
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.