It's a H728 , as in factory part number 11041-H7280, used aproximatly 1976-1980 for California emmissions. If you look at the second pic. just to the left of "728" is a spot where the "H" should have been. Obviously it's not there, either the mold was disturbed or it was intentionly removed, but like I said careful examination shows where it once was and "should still be.