Hi, I need help on something that seems simple but isn't. My GMC 3/4 ton 4X4 pickup is a 1971 but there's no mounting holes for the mirror above the windshield, only 1972 had no holes because the mirror was on the windshield that year. Is there any other way to tell the 1971 and 1972 apart. A friend said my truck could of been when they were starting to change years, so it would be built as a 1972 but titled as a 1971. Is there any easy way to tell them apart? Thanks, John