An 82 Series 3 or newer, with a serial n4501 or above. That is the beginning of the AMBAC fuel system and an all around heavier built machine. Hyperize it and put a 6 or 8 row head on it and watch it run. An N6 of that era is better. More open rotor cage, two overfeed augers(N5 has 1),30 more HP that has been slowed down to extend life, 45 more bu bin capacity. N6 needs to be Serial n 5101 or higher. Unless you do alot of grasses or weedy conditions the N series will shine highly over the l_M series. I went from an M2 to an N6 and haven't regretted a minute of it and my M2 was a wonderful machine, just didn't do well in sidehills and 200 bu corn.