We had never double stacked helicals but close. We shimmed by 1_4" which would be 1_8" shy of double stacking. We also installed what Gleaner called green stem kit when doing the shim job. The green stem kit included another row of helicals for thresher side and it hooked up the steeper thresher helicals to milder pitch seperator helicals at three locations. Well over 200 machines were done just like that. When we did this we normally removed cage sweep completely as well as all the tin covers. The only hard covers we would install is the one just to left of right concave arm and one on each side of left concave arm. Some machines in some conditions could plug just above left concave arm so we built a tin wall up from left concave arm to about the crown of cage. This would stop the material from hanging and starting to build up a plugged area. There is no promiss you will not ever plug cage so it has to be inspected from time to time. If plugging in some area a guy would have to look close for what is starting the plug (to long of bolts, slanted floor built up with junk, no lean of dist auger flighting into the flow, ect.). The positive flow of material dramatically reduces need for cage sweep. We have never reinstalled a cage sweep but you may not want to discard until you know it works for you. N7s are basically the same as N6s and I believe alot of N5s have be converted to the same as N6s. R60 and R70s with P1 rotor were basically the same as these Ns. We went away from shiming helicals in favor of channel helicals for these P1s. The channel helical is better at controling straw. loewen was making a dual pitch kit that basically matched pattern of flat iron helicals with green stem kit installed. We installed a few of these but now just go with Gleaners channel iron kit. They called it edible bean and green sunflower kit. The kit is broke down into individual pieces these days. We delete a few idems like flow retarders when ordering the kit. We would rather a stationary rasp in belly of seperator side over the retarders that are recommended in kit. I might add that we like to convert two paddle discharge to four paddle system plus if machine has a discharge beater we would want straight notched paddles over the earlier rolled back paddles. I hope this answered more questions than it created. Good luck