its not (NORMAL, ON A SBC) now your engine may run ok if coolant doesn,t leak into the port thru the threaded hole but most SBC heads don,t have a hole there at that location, Id suggest you ask a few questions and inspect a few other cylinder heads , and other ports on those heads before re-assembly, does the other head and other ports have that hole? ID bet the answer is NOT, and its the result of a machine shop SCREW-UP