I'VE BEEN LOOKING FOR A 3858403 BELLHOUSING FOR SOME TIME AND I'VE NOTICED A DIFFERENCE IN THE CASTING STAMPING, SOME HAVE THE 'GM' LOGO AND THEN THE NUMBER, SOME DON'T HAVE THE 'GM' LOGO AND THE STAMPING LOOKS DIFFERENT. CAN ANYONE TELL ME WHAT TO LOOK FOR AS FAR AS PERIOD DATING STAMPINGS? IT'S FOR A 68 Z/28. TY, PETE.