That's the finish I refer to as "parkerized" looking.
After the '70 model year, I never saw any stampings on any lids until maybe the late 70s or early 80s.
I don't have anything on that casting number in my notes.
One helpful thing with NOS Mopar master cylinders from the 71 through mid 70s era, is that they generally have that little tin tag with some information stamped in it hanging from the hold down wire. I see it in your photos, but the angle of the picture doesn't show the numbers stamped in it.
There should be 2 sets of numbers and the letters "PWR" since it is a power brake master cylinder. The 4 numbers are the last 4 numbers of the Chrysler part number.