That one's good.
The oval hole is for the 1927 semi auto Auto Ord or Numrich guns, they fire from a closed bolt and differ completely inside from GI. They were standard mags hogged up so you had to use those, you couldn't just grab mags and take them to a gunfight and win. The drum still fit but there aren't many of those except those of us serious enough to have examples.
Honestly? I'd only go about $20 USD on that one. It's a well worn mag...