Engine Casting Info

I get the 3 March 1969, but have lost the reference that will "decode" the other bit of information these markings provide... help please?

Thanks - George

Block was cast on 3/12/1969 , below it is some sort of indicator , what it indicates ???

Somewhere near that symbol will be a pointer pointing to either D or N to signify on which shift (Day or Night) the block was poured and the circle comprised of a number of dots with a central pointer denotes on which of several pours during a shift the block was cast.