Swapping out my 305 to a ZZ4.
Moving needed parts to the new ZZ4 I see there are two holes right above the oil filter boss; I know that the lower one is for the oil pressure sending unit but what is the other one for?
The second hole looks as though it goes into the block a fair distance, it does not appear that the same hole on the 305 ever had anything to it.

Mounting a mechanical clutch linkage.

So, dumb questions numbers two and three...does that hole extend into the water jacket or oil passages?
Should it be plugged?

no, it goes into nothing.

Yup, just a blind hole.

Thanks guys!