That was my first thought Stalker, but they are a bit smaller than modern 44gal caps and the holes had me confused, they could be to seat a rubber or cork gasket. I guess a lot can change in 70 years.
It is interesting that they bothered to produce D^D stamped caps for what would have been a disposable item.
My first thought was the same, looks like the same tool notch as modern plastic chemical drum bungs.
Definately from an industrial storage container of some type.