Most times a gun which is 75 years old with no signs of extensive trigger work in the past will be free of most major bugs. If it was a poor design and had given previous owners trouble some gun hack would have altered it by now. I find that most of these single triggers work well until they are fixed. Since you most likely are right that you have a unlabeled Miller trigger then you should be fine. My single trigger NID was a unlabeled Miller trigger and it worked perfectly.