A adjustable precleaner WON'T be of any use to you because they changed the design of the cleaning shoe. All of the grain that does go through the precleaner will have to go through the chaffer before it can get to the sieves. On the 60 series, the grain that made it through the precleaner went directly to the sieves, this is why the adjustable precleaner was an improvement in the 60 series. There is an extra plate that Deere put in that redirects the grain in the 70's in which also makes the first 12 inches of the sieves useless because no grain can get to it but it keeps grain from getting into the cleaning fan, but that's another topic altogether!