I'VE BEEN LOOKING FOR A 3917610 Z/28 INTAKE MANIFOLD FOR MY 04A BUILT 68 Z, AND SOME OF THE MANIFOLDS HAVE THE CASTING DATE, ON THE UNDERSIDE, IN CLEAR VIEW BUT SOME HAVE IT UNDER THE SPLASH PAN. ANY RIME OR REASON FOR THIS? 67 OR 68? BTW I'M LOOKING FOR A MARCH 68 DATED MANIFOLD..ANYONE?