Case Number & Movement numbers

Hello,
My first post here so forgive me if it’s basic. I have recently received a vintage Omega which needs a new glass and probably a service. I removed the back cover which has a number 2903-16. The movement has a serial number 17651216. Having done a little bit of research I found that the case number is circa 1947 whilst the movement number is 1970s. Is this normal or has the back case been changed? Either way I would like to get a new glass for it but I don’t know where to start in sourcing the correct glass? I have attached some pics to help I don’t think it is worth much but it has some sentimental value to me. Thanks in advance.

Thanks, I just had a look on a different website and found this. So does that make it 1959? I really hope so, as that was the year I was born.