If it is the late 67-70 (not early '67) it has uses a 1/2" wrench flare nut, or 5/16" flare nut (hardware store name) and besides the late '67-70's, it will work up to mid-year 1976 Granadas/Monarchs too.
If it is the early '67, uses a 7/16" wrench on the fitting or in other words has a 1/4" flare nut, (hardware store name) it is early 67 only Mustang/Cougar