Sorry I didn't read your question closer. Click on the Attachments button on the left side of your screen and then click on the Gorden Rotor Bars button. Scroll nearly all the way down to the bottom and it has links to the installation diagrams for various combinations. For the 1680 with specialty rotor, you can get by with 12 rotor bars, which is what we have installed. I think we'll eventually add 4 more (one more complete row) to bring the total to 16. If you want to go "First Class", you can run 20 Rotor Bars and 14 Separator Bars. Youll have to leave 6 of your original Specialty Bars on and 4 Kicker Bars. To decide which way to go, consider your current performance. If your current grain loss is acceptable, but you just want to increase the threshing ability for wheat, I would suggest starting with 12 Rotor Bars and 3 cover plates. It made a world of difference in our machine, and probably will be all you need to do. If you then decide that you need to cut the rotor loss down, you can start adding more Rotor Bars and Separator Bars to get maximum performance. This would probably be helpful in high yielding Milo where Rotor loss becomes an issue. Keystock grates would be another way to cut rotor loss in Milo. We run one in the very rear position for all crops because we hate to switch them in and out. I think the term for our condition is lazy. Two slotted grates and one keystock grate seems to be a decent combination for us all the time, but of course we dont have corn. Either way you go, I think youll be happy with the Gorden products. Remember that these bars let you run the vanes at a shallower angle because the bars pull material through the rotor more aggressively. Good luck, Mike