390 Block Identification

I've been looking around trying to see if there's any information available to help me identify my block and haven't had much luck. My heads are fine 68' 390 GT but the block is odd. It has the following located between the casted screw heads.

"1W"
"ÏJ23"

These are the only markings located under the Oil Filter. The only other item is that the block also has ribbed sides. My best guess is a service block or something out of a truck?

Would anyone have any idea what it my be?

Thanks,

Ron