The second crack is along the bottom outer right edge.
Bayonet lug - "SI" - Inland
Rear sight - "H" in a shield - Rock Ola
Stock marked with an ordnance bomb and an IO in the stock cut out. Stamped MRC (Mount Rainier Ordnance Depot Rebuild mark) on the side of the pistol grip, large ordnance stamp on the stock that is sanded pretty heavily - Inland
Hammer - "LT-Q" - Quality Hardware
Trigger Housing - "NL-Q" - Quality Hardware
Slide "PI" (underlined) - Inland
Magazine catch - EP-Q - Quality Hardware
Safety - "M" in a horseshoe (circle) - Postwar?
Trigger - "BOE" - Could be "BOB" no listing for triggers under either but Quallity Hardware for sears
Bolt - "AI" - Inland
Recoil plate - "W" -Winchester
Handguard - "W" - Winchester
15 round magazine - "KSG" - Saganaw Steering Division
30 round magazine - "MADE IN USA" post war commercial?
That's as far as I'm willing to take it apart for now.
So it appears to my untrained eye that all but the 30 round magazine are US GI at least. Mixmaster though. Sling is not WWII either.