There is really nothing special about any Magnum block until you get into the Mopar cast iron race blocks, but those should identifiable with a casting number starting with a letter P and will have the large letter R cast into the front of the block under the passenger side head deck surface.
Your casting number is typical of 5.9 Magnum engine blocks. The Date on the right side everyone keeps mentioning was easy in the old LA blocks because it was a conventional calendar date like you would normally write on a check. The "date" on yours may be a julian date instead of a calendar date. I am not sure. but there is a pad on the front of the block under the left cylinder deck surface that should have stamped numbers. That will tell you more info about what your block is, or what it came from. I will attach a chart below.