Casting numbers on zl1 block

[Js22644]

I just bought a 3946052 block that was used in an old 69 race car. There is no date code on the left motor mount area and the block has been decked so there is no code to find. There is a casting code on the back of the block that reads KLPT  CST. Can anyone lead me in the right direction to decode this?

Thanks
James Smith