do the last six digits match the VIN of your car? The first few tell what the make, the year, the assembly plant.

http://www.yearone.com/updatedsinglepages/Id_info/pontiacengineid/pontengid2.html

Along with the YX, there is a casting number on the rear of the block, passenger side, just below the head. It may be greasy but is easy to read if wiped off as they are raised numbers.

The date code cast just to the driver's side of the distributor is the last piece of the block info.