Date code stamped in block near PMD

I have a 506 block, 1255506, E148. Figured it to be made May 14th, 1998. The code I'm referring to is actually not stamped but appears to be etched in in the block. Up front on left head bank next to the Inj Pump PMD. Reads YDD 05 27 J8. I figure the 05 27 refers to May 27th.

So what is the YDD and J8?

Thanks

Assembly line info (date, shift, crew, etc.). The date may be correct (2 weeks after casting isn't unreasonable), but you'll need an original Dick Tracy decoder ring to make sense out of the rest. I've heard several explanations, but none of them the same, and they are not consistent from plant to plant. Your guess is probably as good as theirs, unless someone chimes in who actually worked at that plant, at that time.