Unmarked trigger housing....

[painter777]

Wait Mitch...
Don't overload old minds.
I have your Flicker album open.
The trigger housing is a Type III and has been fairly heavily sand blasted, probably why we can't see the marking....
But: When looking at the rear of the housing it has the milling we see from the National Lock for QHMC housings: NL-Q....
But the NL=Q's didn't have the Fish Hook milling from the ledge up the rear of the mag wall.
Yours has the Fish Hook. My best guess because of the milling style I see on the very rear spine of your housing is you have a SG (Saginaw Steering Gear) Type III housing.
Now I could be wrong... But I believe I've got it

Yours pictured below, look for the nearly blasted away letters SG stamped on the upper right rear... below the top receiver lug.
It could be stamped sideways with the G above the S in a vertical position. Not the norm, but sometimes seen this way.

Look Close..... Real close