A machinists level that I can't find another to compare it too

I found this level while cleaning out my wife's shop building in 2017 after Hurricane Harvey hit the Texas coast. It is a Stanley 24" machinists level made of iron. After some cleaning it appears that it very well could have had a chrome finish at one time. The vials have covers over them and the only identifying marks I can see is the number 3 on one end and the letters/ numbers- XC111N. It is iron not cast iron and was made somewhere before 1981 as far as I know. It belonged to my wife's father who passed away in 1981. He was a Boilermaker by trade so it makes sense that he would have owned such a nice tool but, it is unique by comparison to all of my research this far.