645 (6 - 40inch rows) uses the same header frame as a 843 (8 - 30 inch rows). IF you wanted a newer head, you could buy a 893 and reset to 40 inches. Would require a 40" poly point kit Deere sells. OR - you could buy a 645 or 843 and re-build with Deere's 40 series replacememt plastic. Rebuilding a 843 would give you two spare gear boxes in case you broke one during harvest. Just a thought.
