Slant 6 Block Crack

pishta, I'm glad you said it first JB Weld it !
Clean, clean, clean and drill the crack ends at the block with a small drill bit to stop further travel.Stud hole add JB to the cracked threaded area and re-tap after it sets up. I fixed a Pontiac Iron Duke with a busted head boss that way same as yours into the water passage.
BUT if you are going full blown into a performance build,look for another block.