To find out what year it is, check the partial VIN # stamped above the oil pan on the passenger side. The first number in that is the model year for the vehicle the engine came in.
The 5 at the end of the casting number is irrelevant to you, it refers to a mold not a year....
The casting date for the block is on the passenger side of the block (oil filter side) above the clock. that is when the block was cast at the foundry.